This could be a useful thread but could also open up a whole can of worms. There's a possibility of putting new people off if they feel they may be labelled a bad owner for doing something that we do not advocate, plus many of us here, to be fair, have made mistakes.
My biggest mistakes with piggies was not enough research when it came to my first pig's repeated bladder issues. I did try two vets after the first prescribed round after round after round of Baytril (I booked with another to see if she would do anything different). She prescribed more Baytril so I assumed that was all there was. She then operated on her to remove some bladder cysts but this killed her. Personally I now believe that this was not the best treatment for her.
It's not fair to call yourself a bad owner after trusting your vet, so I forgave myself for that, but I have since learned that not all vets know much about guinea pigs, and I will always have regrets.
The best things to do:
The number one best thing to do for any prospective pet owner is
research research research, but research on
pet forums. Do not trust pet shop advice.
Note: Remember even with research we make mistakes. Example: My hamster died because of a mistake that both I and the vet made. She was a very active hammie, then one cold morning I found her shuffling around stiffly and randomly in her cage with her nose down. She looked like she was dying. I rushed her to the vet who informed me that she was dying, so I reluctantly agreed to her recommendation to put her to sleep. Very soon afterwards, on the forum that I regularly used and used for quite some time before getting her, I read that when they go into hibernation they often don't just curl up and slip into a deep sleep, they often go through a stage of shuffling around, stffly, looking in pain, just like my hammie. This had been a cold morning but both the vet and I had dismissed hibernation. All she needed was warming up. We killed a healthy hamster, and I couldn't forgive myself for a long time.
So remember , even when you have researched your pet very well mistakes can happen.
Don't label yourself a bad owner if you have done what you can for your pet with the knowledge you had at the time. We all learn, and we keep learning even when we've already learned a lot!
Practices best avoided:
Things I've seen quite a few times, and seem to be common, often because of bad advice or misconceptions about piggy welfare.
Husbandry practices from decades past
Looking back to your childhood and how hutch animals were generally kept, and assuming this is the right way. No need for me to list old mistakes, but let's just say times have changed as knowledge has grown.
Unsuitable cages
Guinea pigs need comfort. Wire floors for example can cause serious foot conditions (look up Bumble Foot). These conditions cause pain, stress and even death.
Guinea pigs need and appreciate comfort, and luckily there are plenty of ways to provide this. Piggies are unusual in rodents in that most of them don't chew material to bits, so fleece products, nice and warm and soft, are very suitable.
Rule of thumb: If you could scale up their environment or if you could shrink yourself down to their's, would you be comfortable? Would you be too hot? too cold? Cramped? Uncomfortable? Bored? Dirty? They have similar needs to us in this regard. Is their accommodation draughty? Damp?
If a mini-you would be uncomfortable in their home, the chances are they are too!
Small Hutches/Cages. Let's be fair here, this is very common and well-meaning owners do this too. I blame both pet shops and books. I have several books, some of them published several decades a go to be fair, but are still sold to this day as being 'excellent guides to guinea pig husbandry'. Almost all of my books recommend small accommodation. Quotes such as "2 square foot is ideal for a pair" and "guinea pigs should be housed in small hutches because their eye-sight is bad and open spaces scare them". Shockingly bad advice but it's out there in abundance. Pet stores and cage manufacturers both claim that 80cm cages are fine.
If you have a small cage don't beat yourself up, my friend has her's in a 100cm cage which she shuts at night. During the day the piggies run around the kitchen and jump in and out of their cage. Lots of people have adapted small cages with attached runs. There's ways to enhance your piggies environment and expand their world
A permanently large cage is the ideal. The larger, the better
If all you can fit in is a small cage and you cannot adapt it or let them run around, then it's best not to get guinea pigs until you are in a position to provide more suitable accommodation for them.
Cage Size Guide
Overcrowding
You can view this as being connected to cage size. More pigs need more space, else they will likely become annoyed with each other. They may even fight.
Wrong combinations of pigs - gender, numbers
Too many boars: A pair will often work out well. They may fall out in their puberty months. Adults who choose each other by a process called boar dating are often very stable. Three or more boars usually end in fall-outs - expect fall-outs with three or more, you are lucky if they don't.
Lone pig: There is a misconception out there that boars always fight with other boars. This is not true. A pig of either gender may not get on with his or her cage mate, but it's very rare that they actually want to be alone. The vast majority of pigs crave company of other pigs.
Boar and Sow: Expect babies unless one of them has been neutered/spayed. If this has been done it can be a very good combination. A neutered boar and one or more sows is often a very good set-up. Do not put another boar in there though, the two boars will fight over the sows. Note: Wait six weeks after neutering a boar before placing him together with the sow/s. Latent sperm can live for up to six weeks and pregnancy is still possible.
Behaviour and Bonding
Which brings us on to:
Breeding: I'm not going to claim it's out-right wrong. If we didn't have the genuinely caring small-scale hobby-breeders then what are you left with? Back-to-back mill/intensive commercial breeders, accidental pregnancies and inexperienced and indiscriminate breeding from owners who get out of their depths with it all. Please leave the breeding to those who know what they are doing. A caring breeder never does anything large scale, is not for profit, and only ever lets her sows breed a few times in their life. They will know about genetics and of how to minimise the chances of the common complications that pigs suffer from in birthing their litters. Without these careful ones (and note not all hobby-breeders are good) the genetics of pigs are likely to go down-hill. Don't get me started on the other categories, they are often devastating for the health and wellbeing of the pigs involved - deaths, deformities, stress to name a few. It's not for me to tell you not to set yourself up as a hobby-breeder, but do please remember that there are plenty around already, and far too many pigs in rescues needing homes. Remember also that breeding is a minefield of health issues and genetic birth defects, you really do need to know what you are doing. Can you house them all? Afford all the vet fees? Rehome them? Think very very carefully, there are far more pitfalls than you may think and plenty of piggies around already.....
https://www.theguineapigforum.co.uk/forums/pregnancy-baby-care-and-sexing-no-breeding.11/
DO NOT BUY ANIMALS FOR YOUNG CHILDREN. i mean i hope it's okay to put my age but i am 14 now and it makes me physically grimace to think of what sort of awful life those poor little things had. I MISS YOU BEN AND CHARLIE AND I AM SORRY! (they were only about 5 when they died). 
ch when i was a kid lol....
