Have a look at this auction website where oddball Procol Harum items occasionally show up, as the illustrations on this page indicate. They're infuriatingly hard to read, of course, because such advertisements are deliberately kept lo-res: otherwise punters would simply keep the scans and the vendors would not be able to part them from their money.
The poster illustrated here had a bid of $120 on it: it's from the Fillmore East, and is for a Procol Harum, Poco and Mungo Jerry series of concerts October 29, 30, 31 and November 1, probably 1969. There are literally hundreds of categories of objects for sale (from memorabilia to weird). You can search by subject (Procol Harum) or you can click on a specific category (music, records) and then bookmark it so you can easily get back to it again.
It's easy to get seduced by the range of idiotic things, thinking, "Hmm, I'd like that," as you'd select a candy from a box of assorted chocolates. Only after you've swallowed do you remember how bad it is for you!
You can't buy or sell until you're registered with the company, which entitles you to a password: this registration is free. These precautions are intended to cut down on bogus activity. The company also operates a 'rating' system so that anyone who isn't ethical can be easily identified and avoided.
It's really hit or miss bargain-wise. Collectors flock to sites like this, so quite often there's frenzied bidding on a rare old item. But some topics attract less passionate interest than others. Some items have no opening bid or 'reserve'. Wish something apocryphal like this paperback would magically appear there.
For some people ebay.com is just like having a second job. They find some junk shop or thrift-store oddity for a dollar, post it ... and sometimes get $30, $50 or more, which, at the very least, can cover the week's grocery bill. An interesting example of how the Internet has changed things: it used to be that you could comb the countryside and find na´ve shop-owners selling off items for very little. But now anyone with a computer can get sophisticated very quickly.
With Procol items, it seems that there are only a few bidders and fairly modest prices: no real last-minute bidding wars. This corresponds with Matthew Fisher's estimation of Procoholics as being fairly pleasant, mundane, mild-mannered people! Too bad there are not more Procol items ... but (with this publicity) sellers may see Procol stuff start to go for bigger prices, and be moved to put up more and more of it.
It's mostly American sellers, and occasionally they refuse to sell overseas (too much aggravation and time to go to the post office, weigh the item, then e-mail back and give the correct postage, then get a check that must be converted). Otherwise it sounds as though a splendid time is guaranteed for all.
As far as selling Procol Harum items is concerned, of course, fans might like to remember that there's also a ready audience of on-line customers at the Procol message-list or, indeed, at BtP's own interactive 'Beanstalk' forum. Thanks to Ron Smith for the information on which this page is based
More items for sale