You get what you pay for when it comes to paintjobs, so I'd recommend doing the prepwork yourself.

It's a pain in the ass, but if you do it right, it's one less thing to worry about, especially if you're getting a free paintjob.

Do a google search on prepping a car for painting, and you'll find some useful links showing you what you have to do (most links will give you basically the same info, so read a few to get the gist).