Hi - I'm not always super happy when dealers and shops post on forums, as mostly they are only interested in what things are worth, but I know Brighton Guitars is a small independent shop, so I don't mind giving feedback. Besides, I'm sitting here waiting for a builder to come (and he's half an hour late already).
I think a lot of people who are interested in weird old guitars (ie not Fender + Gibson) are prepared to buy online because you can't just go into town and choose one off the rack - they are prepared to take a risk to get what they want, though the situation is not great. I think people are less inclined to buy Fender /Gibson type gtrs online and take that risk if they have access to shops they can visit, but that's just a supposition, I don't really know.
A frank description with details of the good and bad points of a guitar are important, bearing in mind what the buyer can work on and improve and what they're stuck with. A lot of sellers operate a don't ask/don't tell strategy, to take advantage of people who don't know so much about old guitars, especially on ebay. Don't use euphemistic language like 'it might need a little work to bring it back to its former glory' - say what that work needed is.
If you get your info online, link to the info so the buyer has as much info as possible.
Good sharp photos in natural light are essential, but you don't need to go crazy unless the gtr is worth a lot of money.
A video would be good, but stick to demonstrating the sounds and settings with chords rather than just soloing and showing off. A video of a weird guitar with unusual pickups would definitely need a video, because the buyer needs some reference for what they are getting, but anything with humbuckers or strat style pickups, probably not worth it. A lot of people will change pups anyway.
Offering a refund/ return period on online sales will help to allay buyers' fears. Again I'm only speaking for myself, but it might apply to others also - I don't really like buying guitars from shops; when I was young I always felt that shops are just out to rip you off - admittedly this is in the days of the mass produced Korean LP copy, but that slight uneasiness has stayed with me.