I was wondering if it's acceptable to have a stamp in the first page of a book that I'm swapping.  I bought the book at a book sale at a library and they stamped their name in it but then put a 'd' over it when they decided to sell it.  Is this acceptable or should I not post it?

Thanks!

Yes, it's common for libraries and used book stores to stamp the inside cover or first page of a book. It's perfectly fine. If someone wants to avoid getting a book like this, they have the option of saying so by using the requester conditions option.

From the help center:

Decirculated library books may have various markings and/or stamps inside or outside or on the page edges of the book; this is OKAY.  These may not obscure text.

What they said    a library stamp does not make the book unpostable.