I'm a bit of an outsider in this aspect, I don't imagine I'll ever sell anyone here a pin, nor do I think I'll buy one from anyone here - the logistics and the distance pretty much make it impossible.

I don't want to upset anyone, and if my advice is not welcome, I've not got a problem if someone deletes the post.. but I have opinions on the subject, having done lots and lots of deals.

I don't understand why the forum needs a checklist, though. There are way too many variables here.

A flipper rebuild can be subjective. Did you install a rebuild kit? Did you file the plunger and the stop? Did you use the kit from this retailer, or that retailer? Some retailers have more complete kits than others, some have more accurate kits than others, etc.
Was the game re-ringed? The answer yes could mean 2 days ago, 3 months ago, you changed all the rings you can 'easily reach' etc.

Any of those questions are completely objective. There's no way to get a concrete answer.

At some point, a buyer has to take responsibility for their purchases. Do a little work. One of the problems we see over here in the states is what I call the 'walmart mentality' - meaning that people think they can return anything purchased anywhere anytime, instead of doing their work on the front end and verifying what they are buying fits their specific needs, the level of quality they desire, etc. And on the rare occasion when they end up buying something somewhere that won't let them return it, or they get buyers remorse, they raise a stink and draw attention to themselves and in some cases, expect the government or organizations to intervene :)

I think a post or thread about how to buy pins might be more effective. Suggestions on what a buyer might want to look at, questions they might want to ask, ask for references, etc.

If you can't view a pin yourself prior to buying, you should ask for photos of specific areas. If you aren't sure what those areas are, ask someone who owns the game.
If you can't view a pin yourself prior to buying, try to find a forum member that is trusted who lives nearby, and ask them to inspect.
A seller who is selling an item should provide plenty of photographs of their items for sale - flaws and all!

You wouldn't go down to the car lot on the corner, sign the papers and hand them the money without seeing and driving the car you are buying. You wouldn't go to the electronics store and buy a bigscreen tv without watching the demo unit, you wouldn't buy a house without seeing it and having an inspection.

Why would you buy an expensive pinball machine without doing some research first? Yet people seem to do it all the time.