(PS - You DO know I am playing Devils Advocate... right?)
I know YOU are. But some people here just got an idea and are already placing orders with noice....
I've only once found tokens/quarters in a coin box. I find them at the bottom of the cab... in the bezel area... CP area... etc. Those have been paid for but not used... right?
I thought about those, and left it out because it muddied the water. I would say bezel area and console are a definite yes. They didn't bounce out of the coin bucket and up 2 feet. It was paid for, lost, and remains unused. The bottom is 75/25. Could have been one from "on the glass" or a coin mech misfeed. Or it could have been dropped by the operator during collection. All in all, odds are pretty good it wasn't used. Now if you find a thousand of them down there, that's a different story...
You're making an assumption that they were used in gameplay at the arcade though. If someone purchased a bunch of tokens (say someone bought 1000 Flynn Lives tokens from ElecTRONica or something to use in their personal arcade) and then sold a game with those tokens in it, would it be OK to use?
Yes, and that is the assumption a "reasonable person" would make unless they knew otherwise. The collector buying specific commercial tokens for use in a home arcade doesn't happen in 99.999% of the cases, so unless you had specific knowledge it's just a self-rationalization for theft.
But lets use Namco as an example. You buy a used game from Namco arcade, there's 5 bucks in Namco tokens in there. Again, Morality aside, legally speaking, since the tokens were purchased from Namco (as the machine and all of it's contents were bought from Namco) legally speaking, I would say it is perfectly legal to use said tokens in Namco Arcades.
In this very specific case, you could argue that Namco sold you a game and tossed in tokens for use in their arcade as a bonus. But that gets back to the whole "found $X in a game, must I tell the seller" debate. Which at it's core is all about the sellers intent vs.their responsibility to empty the machine.
If it were me, I probably wouldn't do it. Not for fear of getting caught, but because I run a business and so does he/she. I expect to be paid for my services, and a extend the same courtesy to him. If you bought the machine directly, it's a coin toss. Use your own judgment. But if you bought it second or third hand and are now making lots of assumptions about how/why they got there, you are rationalizing why you aren't stealing. And if you have to ask....