I'm sure this has been asked/answered before, but I must have missed it. 

If I say I don't want the book, do I go to the end of the WL queue?  Or do I keep my place and get another offer when the book comes up again?

You will go to the end of the line.  You also have the option of posting a thread in the Book Bazaar forum asking to borrow a credit, and then returning it when you are able. 

Gavia,

pm'd you.

Thanks for your replies - I now understand better how it works.   There are some extremely kind people on this forum who have offered to give me credits for the WL book.   But I realize that I phrased my request incorrectly.

The truth is that I actually do have enough credits for this book, but I have a disabled friend with no money for whom I've been getting books, and I didn't want to spend the credits on myself and then not have enough for something she wants.

In any case I have accepted the WL book, as I figure I really can afford the one credit that it costs.

I have returned the credits to those who sent them (I think), and I thank you again, so very much.

To clarify - the book is removed from your Wish List completely if you decline an offer and you then need to add it back on. That is how you end up at the back of the line.

If you don't have the credits for Wish List offers right now you should go place all the books that are close to offers on Hold. You won't get any offers and you retain your place, continuing to move up with the line until you get to #1 and will remain there until you unhold it and are able to accept offers. 

If you're saving your credits for the friend, you can individually put the books for you on hold so you'll hold your place in line, but be skipped over if you get to the number 1 spot.

Ok, thanks.   It's good to know there is a way to not end up at the end of the line.  I have a few books I will put on hold.

To add to what Britney said, if you make it to the #1 spot and have the WL book on hold, you'll be in the #1 spot whenever you take it off hold.