Buying guinea pigs involves lots of the same processes as adopting one: you’ll need to make sure that you have all the right equipment waiting at home, water, fresh and dry food, a (reinforced, air-holed and lidded) box that won’t slide around, and a proper route plan for getting your new pets home as speedily as possible.
Check their surroundings to make sure they're being kept in good conditions before you purchase one
Once you’re home, put your guinea pigs carefully in their new hutch and make sure they have everything they need. Then, crucially, you’ll want to leave them in peace for a week so that they can properly settle into their new home. This means that you’ll need to make sure no one handles them until about a week has gone by and they’re all settled in.