That sounds like a decent price. Is he dropping them off and picking them up as well? At that price I would require that they pay for needed parts like you said. Any board work would be extra and there would be no timeline to get it done either. Drop them off and I'll call you.

$500 seems way cheap for a full tear-down.

The one thing you will NEED to do for sure is get a written contract. Spell out hidden damage/repairs, loss from flood/fire, how you will inform him of any needed changes. Spell out EXACTLY what you will be doing and not doing.

That way there is no misunderstanding, no arguing, no bent dicks.

For one you are calling a rebuild a restore which is way more involved.
I have been asked to do this and always decline, just not worth the headaches.

I agree with Vid, write down everything you know is wrong and will repair, clean and recondition. That way if you find something major that is wrong or made of unobtainium, you can explain that you can't fix that item or he will need to find the part/pay extra.

Track your hours in a day/time type log and show that to him at pickup so he understands what a deal he got and/or so you know how to price future projects.

Dealing with someone new can cause issues with expectations. He may say its no rush now but when you are 3-6 months in and still not done because your regular life got in the way, he may get upset so you are better off setting that expectation up front. Like you said, when you do this on a pin you bought, there isn't someone waiting for it to be completed!

how in depth of a restoration you doing? or you just doing a nice in depth shop job and fixing errors?

I have considered doing this over the winter months here in West Michigan but do not think anyone would be interested. Not sure that $500 is worthwhile for 50-60 hours of time invested especially if customer headaches were tossed into the mix, If you knew everything would go perfectly hassle free I could see it.

but at the same time, I would put 100+ hours on some playfields and only got $500-600 back in the day. and that was including clearcoating costs. Needless to say, I had to increase my prices the past 2 years.