On ebay you see a lot of estate stuff pulled out of a basement and listed as is. The seller doesn't care.
Vintage be careful. Surface dust is fine. If it need a cleaning leave it alone unless you know how to clean it without harm.. No windex. Just a damp cloth, if its dirty use a warm soapy lent free rag. Pull the knobs and soak them in ivory. Dry and any tough stuff just use baby oil and work off the grim with CLEAN soft lent free towles. and cotton. Never Dull is great..
OR throw it in the trunk take down to the car wash and preassure wash it..:-)
Perhaps this is good thing, they expose the truth. Cleaning up and polishing may hide how they truthfully keep equipment.
On the other hand, dust and fingerprints may not indicate true condition of internal components. It does show someone not understanding or caring about marketing of products. Buyer should expect discount price for risk of purchase of such equipment.
I just sold a bicycle on Ebay and aside from a few obvious scammers I had a great experience as did the fellow who purchased the bike. I do think you are better off selling Hi Fi gear on Audiogon for rather obvious reasons.
There are many people out there that are, for lack of a better term, slobs. It does not occur to them that dust and dirt are a problem. They grew up in such an enviroment and they see it as normal. I think you can expect them to be more careless with their equipment and I would shy away from it particularly turntables, tonearms and cartridges. I do think the majority of us are meticulous with our gear.