To support getting a fair price for your painted minis, I find that photograph quality is very important for a good listing that will get bids. Harsh lighting (unmodulated flash) can make even well-painted models look terrible. If the picture is too dark or too blurry, buyers will pass because they don't want to take a chance on what the item actually looks like.
SO true. I've passed on A LOT of minis for sale on eBay because I couldn't really determine the quality. Similarly, a lot of my photos of my minis make them look, IMHO, much worse than the actual paint job b/c I don't know how to light them properly.
Be attentive to details: clean your models well and use decal medium. I'm gun-shy about buying pre-painted minis now because I've made several purchases where the paint job looked like it might be okay, and then I got the minis and the painter hadn't bothered to remove flash or mold lines. I also see photos where there's shine on the decals. I realize that attention to these details is very time-consuming but I don't want minis that aren't given this care - maybe there's a market segment that doesn't demand this, dunno. But if you DO do these things, advertise them! If I saw listings where the painter advertised that s/he cleans the models well before assembling and makes sure there's no shine to the decals, I'd think: "There's a seller who cares about quality."
I imagine you're in a better position if, as you say, you're not in a hurry to sell them, b/c the market fluctuates wildly. You have to wait for the buyer who needs what you're selling. Market demand seems especially low right now - I assume because: 1) the people who play have most of what they need, 2) lists have been playtested to the point where everyone knows which units are most effective (and have obtained them) and 3) b/c there don't seem to be many new players (hopefully all that will change with v4).
I don't know this for a fact, but at this point in the evolution of the game - with relatively few new players picking it up - I would imagine painting up the newest, sexiest units as they come out would drive sales.
If you can paint infantry fast enough to offer them at a reasonable price, that would seem like a good niche. Attractive infantry basing goes a long way (IMO, bases are what make infantry "pop") and flattering photography is even MORE important with infantry. For my tastes, I look for high contrast (distinctive facial shading, highlights on raised parts of gear, etc.) Military colors already fade into the background (which they're designed to do) but we play minis games to admire our minis on the table, so my personal taste is for minis that look reasonably historical but that compromise this a little to "pop" on the table.
Master a few different painting styles and then offer to do touch ups on your models to match what the buyer already owns for a little extra charge. I don't give most listings even a second look because the style in which the minis are painted don't match the style in which my large, existing collection of stuff is painted. I haunt eBay and I've pretty much IDed which of the regular sellers of painted minis have stuff that works with my collection and which don't. For myself: if more painters promoted a service that accompanied their sales offerings where, for a reasonable added cost, they would do some additional detail painting - solid-line highlighting, black-lining (other people might want weathering) to make the style of their sale minis better match my collection, I'd buy a lot more painted minis. B/c, on the flip side, If I have to do detail painting or other finishing on pre-painted minis - the most time-consuming part of the whole process - then I might as well paint them myself (Of course, IMHO, I'm a pretty good painter - I know people who play games like FoW and don't know how to, or don't want to, paint).