Try going to ipdb.org or pinside.com and read the game reviews

Also try setting up pinmame and download the games where you can play them on your pc to get a feel for them - some play better than others eg Star trek next gen is a dog on pinmame but an excellent machine

Keep an eye on 4 sale section on this site or Aussie arcade- much better off buying from a member than a dealer in most cases

Don't be afraid to ask questions, try find and play the pin youre interested in before committing

You are probably better off getting a couple of pins rather than spending all your cash on one high end pin