I am still pretty new.  I have left the price stickers on for all the books I have sent out.  Is that an acceptable practice?

yes, stickers(on the outside) are okay as far as book condition... if some one wants a book with no stickers they need to have a condition stating that.

Edited to add: Some of my books have "PAID" stickers on them b/c I work in a store that sells books and if I don't have a paid sticker, I could be fired, I have not had any problems or any receivers complain because of this and the help center does not forbid stickers. 

I am waaaaaay too lazy to peel off price tags.I am glad that is not verboten!

Gee, I hope so:)  I don't usually take price stickers off books that have them, so much effort ")  I figure I'd ruin the book if I took them off, I'll leave that to someone who will take the time to do it right:)

I used to take the stickers off but discovered the residue sometimes left more mess than a sticker does!  

The books on this site are supposed to be used, so IMO a price sticker is harmless.  If I want to read the book, a sticker on the cover won't bother me!   :o)

The only time I do it now is if it covers the ISBN no. on the back-then I only take off enough to read underneath it.