It doesn't look to me like bumble foot, usually the abscesses are directly on the paw pads rather than the legs because their legs aren't making contact with the wire. It looks more like a tumor to me however I am not a veterinarian
As Ghostinshow said, a lot of pet stores have a guarantee that if you adopt a pet from them that gets sick or requires vet care in the first few days that you have it the store is liable for the bill. So if you do want to adopt him that is something to keep in mind
