I wouldn't say guinea pigs are tough... in my experience, guinea pigs are pretty frail for animals that size. If they get ill, they tend to go downhill really quickly. If they feel unwell, many will go off their food and otherwise make their situation worse in a hurry. My vet has said before that a lot of guinea pigs get ill or uncomfortable and just give up... most of them do not seem to power through pain or illness very well. That said, I had one pig with a ton of health problems who never stopped eating, never changed her behavior in spite of certain pain, and lived to be almost 7 in spite of at least two serious, chronic problems. My vet said she had the heart of a lion in the body of a guinea pig! But she's the exception to the rule. I once thought that one of my pigs had had a stroke because I got up one morning and she was laying stretched out, rolling side to side, wouldn't stand, wouldn't eat... I thought she was dying. I got an emergency vet visit that morning, drove to the vet crying, was afraid she would pass way in the car on the way... turns out she had a bladder infection. She took antibiotics and lived another 4 years. She was just the exact opposite of tough! LOL!
As for nails, yes vets will clip nails for you, but it's really not that hard to do it yourself at home if you like. Also, at least in my area, there are some local pet businesses that have 'nail clinics' where they will clip nails at a lower cost than the vet once a month (not sure where you live, but the Pet Valu near me has a monthly nail clip clinic that will take guinea pigs and rabbits, as well as cats and dogs.