I'll quickly throw my .02¢ in on this issue...
I bought a 1.5 yr old Mutoh VJ-1204. The printer was a repo that looked like it never had used it's first ink cart. However, the supplier (Rayco out of Chicago) had replaced the head, capping station and dampers and basically brought the thing back up to new specs. I can say it was definitely a wise choice as it saved me several thousand $$ over new, and got me into the printing game much sooner than I could have with a new machine.
Fast-forward 2 years later and this thing still runs like new with the same printhead, capping station and dampers. I'm sure some of these things will need replacing soon enough, but I am also very particular about my machine and it's cleanliness. Again, I'm not a big shop who runs their printer 1-2 shifts per day, so it's not getting that kind of abuse.
Not all sign shops are equal, and thusly you can't make assumptions based on printer usage. Go inspect the machine, take off the covers, check for cleanliness, do a print check, run some of your files, ask questions - lots of questions, make them show you how to maintain it, where they buy their parts, ink and supplies from. Chances are if they are trying to hide something you'll be able to sniff it out. Don't buy something sight unseen for what seems like a miracle deal expecting it to be like new. Expect to have to replace a head, capping station, dampers, etc. If you don't have to, it's a bonus, if you do, you were expecting it.