Is there even a market for buying painted stuff?
I was looking at painted 28mm Napoleonic stuff on eBay recently and there is certainly a market and the buyers don't seem particular about the quality either. There was silly money being paid for very sub par paint jobs.
Ignoring the people actually selling off their old collections,
Some people sell 'armies' a set of infantry, cavalry and a gun or two obviously painted to sell, often individually based.
Small groups of individually based skirmishers are popular as are guns and crew (multi based) or officers/ADCs on horseback either singular or in pairs. Basically, anything you can drop into an existing army without needing to change it. Wagons and limbers are popular too.
The big units, often a speed painted box of plastics described as 'beautifully' or 'expertly' painted based on the plastic bases that are supplied with them (Rendera?), seem to be a popular option too judging by the number available.
It's worth having an extended look sometime, it's an odd market.