Ask some of the local bowlers who they go to. If the guy at the lanes doesn't seem very knowledgeable, probably most of the higher level bowlers go somewhere else. Find out who it is and go there. If they go to the local guy, then maybe there's a good reason he didn't share much info with you. He could have taken over the shop recently and inherited these used balls, or he's part-time and someone else took them in when he wasn't there.
Wherever you go, ask if they have any packages for beginners. Many shops will have a deal for an entry-level ball, a pair of shoes, and a tote bag. You could save a few bucks getting them as a package. The ball is usually a lower-end ball like a Power Groove, Scout (I wouldn't get one of the new Scouts since the Ebonite-produced ones don't have more than a pancake core), Tropical Storm, or something like that. If they have a Tropical Storm package, I'd get that one.
SH