Last Hussar
I started this game in the 70s with Hinchliffe and Minifigs being the only two options. After 30+ years the quality of castings has improved. Some like Hinton Hunt and Warrior have come, and almost gone, others like Front Rank, Essex, Perry, Elite, Redoubt & Steve-Barber have come and made a niche.
Some folk will want "old Minifigs", which are smaller than the current mouldings, others want other "Old" figs to make up units or armies that are out of production, experience tells that some folk will pay more for stuff they want. Bidding wars are fun to watch but not to participate in!
If I bid on evilbay, I will not pay much more than 60% of base metal prices for unpainted MODERN 28mm figs, usually because there are bound to be some I don't want or I will have to buy a few more figs to make up a unit. The older figs, I will bid 30 to 50% of current base price. I win enough figures not to have to change this policy.
Painted "old style" figures, will attract bids of roughly base metal, if the photos are good AND the units are useable in any army of mine. Painted modern figs can go for silly money or real bargains can be had. Rebasing is far easier than repainting or touching up, I will almost certainly rebase any figs I buy, just so they match in better.
In short, selling on evilbay can get you silly money for painted figs if the photos are good AND the units are useable AND two or more people want the figures. Don't start the price too high. Look on the trading sites for prices you can expect. Nation is important, French painted as Italians or Saxons will usually realise less than French painted as French.
If your colleague has figures YOU can use, an offer of £1.00 GBP per fig for Foot/Infantry, £2.00 GBP for cavalry and £3.00 GBP per model gun should not mark you down as a cheapskate, but check the scales, check the unit sizes and make sure you don't need to pay £200.00 GBP to buy that 24th fig to finish off that battalion of Wurzburg Garrison troops as the figs are now as rare as rocking horse poo! If you don't like/want/can't-use any of the figs, you will have to resell them, this can give you effectively free figs, if you get more than you pay, however, this is a risk, so don't offer more than you think you would pay. If you don't like them, or they will need painting, walk away.
Finally remember if he bought the figs in the late 70s, they will have cost him about 10p for foot and 25p for mounted.