Originally Posted by robatsu

Some good advice in this thread. I'll add a couple of things I think may be pertinent (and possibly repetitive of what has already been posted):

1) Describe ANY flaws/issues in an item, no matter how minor. You don't necessarily have to have pictures of every ding, but be descriptive ("light scratching on the left brake lever..."). In addition to this, give an opinion in standardized terminology of overal condition - I use poor, fair, good, excellent, and outstanding as descriptors for used items. Be honest about the description but also be enthusiastic about the item in general.
2) Ship stuff FAST. I can't overemphasize this. Doing so seems to innoculate against a lot of problems. Somebody who is tapping their foot waiting for their item is predisposed to be critical of the sale, vs. the guy who is delighted the item is already there. Generally, I try to get stuff out the day after payment arrives at latest and often the same day if payment arrives early enough.
3) Unless is it is something that has a thin market, which is sorta unusual for most bike parts, start your auctions at .99 cents, no reserve. Out of hundreds of items I've sold, I've only regretted this once or twice, and in those cases it was really obscure items. But rather than do reserves or large starting bid in the rare case, I would probably go with a buy it now price.
4) Don't make money off of shipping. Most of my auctions quote shipping prices that are at or a little below actual shipping cost. Occasionally, the actual shipping will come out a little below what was charged. If it is more than a buck, I refund it to the buyer w/an explanation. This delights buyers and, again, tends to predispose buyers towards viewing you as an honest broker should item condition issues (almost inevitable when dealing w/30 year old bike parts) arise.
5) If a condition issue arises, for typical bike part items, I just refund the entire auction with a smile and tell the buyer to keep the part. This is for the typical <100 dollar type stuff. it doesn't happen very often, maybe once every hundred sales at most. Anyhow, I figure it is just the cost of business being a junk reseller. If I think the buyer is overly picky, I then silently put them on my block list. This has happened only once or twice. Anyhow, for the stuff I've been selling, with few exceptions, it isn't even worth my time to get into a dispute w/a buyer.
6) Pack stuff nicely, show the buyer you care as much about the part as they do. Remember, when selling vintage/collectible stuff, your item may be the stuff of dreams for the buyer and the crowning glory to his project even though you may think it is just a ratty old derailleur or something. I use USPS for the most part because they give out free boxes, nice to ship stuff in a new box rather than a beat up old shoe box or something.
7) Respond to all questions/inquiries.
8) Sometimes you might want to hold off on an item. Semi-rare stuff tends to go highest if an instance hasn't appeared for a while. When something like this goes for a high price, it often brings a few more examples out of the woodwork and the closing price will decline with successive auctions. I've seen this pattern time and again. So if you are selling some NOS Maxi-Car hubs, might want to wait a little while if there is a current auction for some or if an auction completed recently. I even have done this with some of my own items of which I have multiples.

Really, most of this boils down to treating people how you would like to be treated. As I've been working through liquidating my bike/parts collection, which turns out to be a lot bigger than I thought, I've ended up with quite a few repeat buyers and I'm certain this results in higher closing prices.