Hi Nealo, yes that surely is a good sign the guy won't sell to just anyone.
Ebay is a great place to buy a reasonably priced cage, a good idea is to check the name of the cage and compare it with the same cage in a more expensive shop, be sure to ask the seller any questions you need to ask about the cage and ask him/her if the cage is like-for-like and compare prices, take into account postage too - this is sometimes free on Ebay cages. Check feedback for happy customers and away you go.