As I look at the bazaar from time to time I notice members selling 50 or even 100 credit. I checked one of these members once and they had no books on their shelf. I thought the member must be accumulating credits in games. That would be a neat way to make money I guess. without contributing anything to the club in the way of books sent. 

That could be true.

As for me, I accumulate more credits by sending WL books out than by keeping many books on my shelf. (However, I have never had more than 50 credits at any time though.)

At the time of "the Change", Feb. 2015, I had well over 400 credits and at that time reduced my bookshelf to about 50 books as opposed to the hundreds I used to have. It could be that the member, like me, has hundreds of credits but does not want to accumulate any more so no longer is posting books or only posting WL books. Members like me contributed thousands of books to the club "in the way of books sent" in previous years but no longer feel comfortable having that many unused credits.

I thought the member must be accumulating credits in games.

Charles, are you familiar with PBS games or participated in one?  I have for several years, and typically the only credits involved are each player providing one credit as a "security deposit."  This credit is held by a moderator during game play, and it is returned to the player when he/she fulfills the promised action (sending a book to another game player).  There's no net gain of credits through any PBS game I've played.

You don't get credits from games. It's like Valerie said, you send a credit to play. You play for books, when the game is over and you have fulfilled your piece..sent a book to whoever won it in pbs postable conditions,  you get your game credit back. You can't play for credits. 

well that theory got blown up.

Could be that they are active on SwapaCD or SwapaDVD, and the credits are coming from there.

Be careful buying from someone trying to sell 100 credits, no member can transfer more than 50 from their account in a month