The pet store didn't sex him, I went to Guinea Lynx and to their sexing page and it was obvious that he was a male. The pet store never sexes animals, unless maybe cats and dogs, but if you ask about it they'll probably lead you through it. I didn't ask. I bought him a huge cage, it's about 10 square meters for him, carefresh bedding, heavy bowls, water bottle, some chew blocks, some good guinea pig pellets, lots of fruits and vegetables, timothy hay and a mineral and salt block. The pet store told me they should have a mineral and salt block. They also told me to get extra vitamins for the water, but I've read too much about that being a bad idea. I have a pretty big backyard with lots of unsprayed grass, and I also have time to take him out daily and supervise him, if need be buy a run of some sort. I plan to get him a friend, but will do so making sure I get a male, if he is indeed male, which I believe he is, I've had guinea pigs before and he basically looks like a less mature male, an i instead of a y, prominently. I'll get a picture as soon as I get some batteries.
I'm also planning to get him vet checked ASAP just in case.
PS: his toenails vary from white to black, some in the back are black. How would you cut black nails...? Just more carefully, maybe doing the clear nails first to get an idea? Or could you hold a light up to them or something?