Hi and welcome!
Here is a link to the most common problems that can come with new guinea pigs; it also includes information on your customer rights in case of health problems. If in any doubt, please see a vet to check for skin parasites or a fungal skin infection ringworm); with a positive diagnosis you can reclaim the vet cost from a pet shop if they are seen within a certain space of time, which differs between countries.
More information in this link here:
New guinea pigs: Sexing, vet checks&customer rights, URI, ringworm and parasites
Keep and eye on the scab. It can be from an accidental swipe but if the area gets wider with a white crust, then you are most likely dealing with ringworm, which is highly contagious not just to guinea pigs but to humans and other pets two and requires a vet visit for proper treatment and very specific hygiene measures at home if you do not want it to turn into a long running very exasperating saga where you ultimately pay a lot more than if you had done it correctly the first time round. This goes for all skin parasites, too. The cheap option is very often the most expensive mistake...
Ringworm: Hygiene And Pictures
It is very important that you save up for vet care as part of your guinea pigs' weekly/monthly living cost. The right to be free of pain and any unnecessary suffering is one of the five basic animal rights. You do want to be able to rush a guinea pig in agony to the vets at any time and also be able to afford any life-saving basic treatment like a course of antibiotics or a straight forward operation. Cost can unfortunately spiral into the hundreds of pounds/dollars very quickly. There is no such thing as a cheap pet.
And since well kept and properly fed guinea pigs have an average life span of around 5-7 years (but they can live even longer), odds are that you need to see a vet at some point or other.
A good diet with unlimited good quality grass hay (about 80% of what a piggy eats in a day), a limited mainly green coloured veg diet of around 50g (carrot is like feeding a bar of chocolate to a guinea pig) and 1 tablespoon of pellets per piggy per day will make sure that your piggies are overall much healthier and don't need to see a vet for any avoidable health problems. Your good care is crucial for the long term, so it is worth reading up on your piggies now and learning about them.
A guide to vets fees, insurance and payment support.
Accessing veterinary care during coronavirus/Covid-19 lockdown
Tips For Vet Visits
Long Term Balanced General And Special Needs Guinea Pig Diets
Getting Started - New Owners' Most Helpful Guides
