If you're selling stuff on ebay legitimately its not really a problem. But since there are so many scammers and sleazy jerks on there, they have to tell the cops when people get ripped off so they won't get sued. Plus, since they have insurance for everything up to $250 they don't want to lose out huge.
If you're selling illegal **** on ebay you're just asking for trouble.
I've bought and sold tons of stuff on ebay and never had any problems, and I never get any spams, junk mail or phone calls from them. Its a good way to unload some junk you have laying around the house without having a garage sale.