I got a hardback book that has a big sticler stuck on the front like 2 x 4 can they post this ? Im not thrilled about it.

Another old school trick to remove stickers is to hold it about an inch over a cigarette lighter briefly (BRIEFLY) and immediately try to gently remove the sticker.  The heat from the lighter softens the glue on the sticker.  You'll be left with some residue, but that can be cleaned off with Goo Gone or some such.  Of course, you'll have to be careful regarding the type of cover the book has and it should be done VERY carefully or you'll have a huge firestarter in your hands. 

Its on the dustcover

Is it a price sticker?  Some of those price stickers from bookstores can be ridiculously large.  Since dust covers are not required for posting, the book is postable. If you had an RC requiring the dust cover, I think it's still postable.  The only thing in the help center dealing with stickers is Book Crossing stickers are allowed inside and outside books.

Stickers are allowed. Library books also have stickers all over them and they are postable here. Used bookstores stick stickers all over books sometimes too.

Dustjackets are not required.

If you have Goo Gone, try that, especially if the cover is shiny paper. Rubbing alcohol may also work.

Yes. There is nothing about a sticker that makes a book unusable or unpostable. If you don't like the looks of a book with a sticker on it you will need to use the Requester Condition option to ask for books without stickers.

Dustjackets are even farther removed. If you don't have a Requester Condition asking for the Dust Jacket, then it doesn't have to be there and therefore can be in ANY condition, doesn't even have to be postable (could have boogers on it and still not make the book a Problem swap). 

I just carefully pour a small amount of Goo Gone on the cover/dust jacket, get a letter opener and peel it off.  Then a paper towel to wipe off the glue and it's all done.  Nothing to it.  I've never had a problem ruining either a book cover or a dust jacket.  Good luck. Pat

A hair dryer also works well. I also use Goo Gone to remove any residual stickiness.

Some of those stickers are very easy to remove, others aren't. I can understand some stores not wanting customers to remove those stickers but... why make it so difficult to remove once the book is purchased.  And why do some store have to put those stickers over the descriptions? This is one of my pet peeves.

I buy Goo Gone and like brands two or three bottles at at time as I use it on books and various stuff around the house. I'm cleaning out my mother's house and she used decorator's putty on so many things that I now hate the putty.

Instead of using a metal knife or other item to remove the sticker, to the point where I can use Goo Gone, I use my fingernail. I found fingernails have less of a tendency to damage a book. Of course, unlike the ladies, I am not too concerned with what my fingernails look like.

I like books so much that none ever leaves here if I can improve it in some way, especially if I can clean up the covers. I use Goo Gone to remove many types of dirt. It is interesting that some types of dirt do not  react to Goo Gone, but a wet rag will take it right off. And I have lost count of the number of covers I've repaired with book tape.