Put clear pictures of the dial fronts and back with the diameter in the description. Back should show the feet positions. I always looking for 27.5 mm dials so keep an active search for such. Start things low. I have a number of dials in my watch list for 40, 60, 80 or more. they just sit there as there are issues with them. So one has to chance the risk what a dial will net.
If I am around the computer I will sweep the new listings under parts and accessories several times a day. Before the tarrifs I had 100+ in my watchlist, now I am lucky to have 45 or so. I did get a rare quartz watch, and did track parts to Europe and Arabia. There is a bezel I need, but gas and bridge tolls has been expensive and I do not have the slop I once did. It now cost me 8.50 to cross the bridge to go the 7 miles to the maker space every time I want to use the laser, so I do that weekly. So the bezel sits as I may be the only person in the world who can use it, but am not willing to pay the extortion and double taxation to get it. Same for a case, in germany where I had to go to austrailia to get a part. If it is the only one in the world, then the demand just is not there no mattter how rare it is. These are not baseball cards.
The other thing is when I sell, it takes a while. and offers are low. I tend to sell bench sweeps, which contain broken bits and bobs, even used empty packaging. So do not put anything in the trash. You may get a dollar or two, or simply make someone happy.
I mostly buy from the same estate sellers, who do not always have the 100 percent rating. It really is about knowing the seller. Lately in the US stuff like you offer has dried up from their sources. It is all about volume of sales. Sell items for a few bucks, and sell hundreds of thousands of them.
Parts also trend, a date corrector may list for 100s, then a whole bunch of them show for 25. So it becomes more about supply than demand.
It has been months since I have seen listings of jumbled watch part lots. AI tells me that 'agents' are being used to cherry pick these listings. Most lots what say omega tend to have a ladies movement in them as a sweetener.
Others dealers part the watches out. This also sits. Some parts are more popular than others, but if money is no object the part can be located. Practicing watchmakers will tend to hoard these anyway. Material houses also have a lot of material for the off stuff. TM Watcho, Paylak. OFrie is pretty much picked over but stuff is found from time to time. There are probably 100s of thousands of estates like your grandfathers, as before the 1990s there were that many watchmakers in every community and parts not restricted. So there are dealers what focus on mining this.
Do not dis the quartz stuff. especially cases (mid cased are identical to mechanical cases in the 1970s) so it is only the backs what differ. Post clear measures of the the backs, the bits what hold the gaskets.
Also look at what has sold. There is a lot of 620 and other ladies materials still sitting idle, as the case were scrapped for metal content. There are also odd things like 710, and 570, which have a lot of spares for short runs of complete watches.
