NJ Marty:
Keep listing until you sell - as long as you don't have to pay a listing fee.
Raise and lower the price from time to time (the "Hawthorne Effect"). I've read that the majority of eBay items are sold with just one bid. So you're tossing your hook out there looking for just one fish.
You never know how people search - or when.
I just got a bid on a book I've been listing and re-listing and re-listing for at least 6 months. Sometimes I re-list right away, sometimes I wait a few days, thinking somebody might be watching and then go "Dang! I missed it." That's why I almost always raise the price on the first re-list. eBay suggests lowering it - but why should I reward somebody who didn't pull the trigger right away?
You also never know when somebody else will list your item for more money and make yours look pretty good (that, of course, works both ways...).
Bottom Line: Re-List!
Good luck to all,
~ The Old Bookaroo