Am I too picky.  Last 40 pages of book were crinkled & had clearly at one time gotten wet.  There were no stains, and completely readable, but in my estimation not repostable. 

I emailed sender about damage,  but was not clear about what I wanted.  He emails back with sorry missed it, "How would you like to handle this ?", and proceeded to tell me how much he liked the book.  Until now, I actually thought credit was automatic when book was received RWAP.

Well, I've been able to press the pages with some success.  But should I have to do that to repost a book?  Or should I just tell him I want a credit. 

You're due back a credit, because there's not supposed to be any liquid damage, whether it stains or not. Stains can be a seperate issue. You need to specifially ask for your credit back.

You don't have to return the book to get your credit back. If they want it back, they should offer you an extra credit for postage or otherwise repay you for posting it to them. (I once just had someone mail me the stamps.)  Whether you want to do that or not is up to you, if they really want the book back enough to pay the extra costs.

http://www.paperbackswap.com/help/search.php?terms=liquid+damage

Overall Condition:

• No damage at all from water or other liquid
• Not soiled
• No stains (exception for cookbooks--see below)
• No mold
• no highlighting, underlining or writing on text pages (exception for Textbooks/Workbooks and travel guidebooks --see below)

You do have to request your credit back if you want it.  You are within your rights to request it but, sender does not have to return it....but, it is your option whether to request it back or not...you won't be able to repost it but, if it is a WL book you could offer it in the Bazaar and ask for a credit or some genre forums have a spot to post WL books and request a credit. 

Credit returns are not automatic when marking a book RWP to prevent people from trying to scam.