As a custom painter, I am seeing this situation a lot. I've had several similar situations in the last two years! Just because a guy can weld, fab metal patches, and spray primer, does not mean he is a "bodyman" or a "painter", who is familiar with how straight a body has to be to hold a nice paint job.

I often see jobs that were not ready for primer... but are primed. The majority of buyers will assume that the car is at the stage that you can start painting. I think part of this is because of the new movement, to start spraying primer before you get serious about the bodywork. Unfortunately, primer does a great job of hiding what might be hundreds of minor flaws. Many buyers may not be familiar with this new theory, and it's common use today.

As long as you don't "assume" that it is paint ready, your will not set yourself up for disappointment. You will also be able to negotiate the price down, by mentioning the fact that "primered does not mean paintable". You will also be mentally prepared to find out that you may need weeks of bodywork, more priming, and more sanding, before you can paint.

My advise... always assume the worst, then you won't have a heart attack, when your painter starts guidecoating and block sanding, and you learn that it is "as crooked as a dog's leg". :-)