Hi and Welcome:
A vintage KA in good shape is a great dishwasher to have, no doubt about it. Many people here have them, and I think it's safe to say most of the KA owners here wouldn't want a new dishwasher.
If the eBay seller does not prove to be a member here (and I don't know of anyone who claims they are the seller), you're going to need to be pretty proactive with the questions before buying one from them. Photos are great, and digital cameras are capable of a lot more detail than they used to be, but even great photos sometimes don't really convey some subtle things, like just how shiny an inner tub is - or isn't.
My own suggestion for greatest satisfaction is to take your time looking, to find just the right unit; your partner might get impatient if your purchase is a dud. Most "other halves" are okay enough with vintage if it causes no inconvenience; some get interested in vintage themselves, and the savings over buying new is helpful, too. But a lemon - especially on the first try at owning vintage - is not a good thing.
Depending on your mechanical abilities and your partner's patience with a little mess and upheaval, you might also consider buying a unit on your local Craigslist and doing the refurb work yourself. This site has a wealth of information, including service manuals. Plus, we have the KitchenAid "magic bullet" - stevet, one of our members who is a walking database of every possible KA ailment and its fix.
You're embarking on a great adventure, and trust me, it will become more fun as you go along. I began some years ago with a pair of Maytag washer and dryer bought because I'd had it up to here with new stuff. I now own all-vintage majors - except for a fridge, and that'll be happening soon, I hope - all of them but the range in daily-driver use. The range is on its way from its old home of Wausau, WI and will be here soon.
Good luck!
