I don't think there's a general trend based on single player vs multi player. Just depends on the title. I've never played Gin, but pictures of the playfield look wide open. Most people don't like that, so the value is probably pretty low on it. Don't pay more than $300 if it's in good condition would be my advice, but I'm far from an expert.
Also it's a Chicago Coin machine and they usually seem to go on the low end of the spectrum, value-wise. You should use that as a haggling point as well.