I had a few packages. Lucked out and got a really friendly woman at the counter. First, she suggested "we" take all the $6.50 worth of stamps off the package and send 

the contents in a $4.95 flat rate envelope, which she did without any help from me. She gave me the savings back in new stamps.

Second, and most shocking, after mentioning that I get a lot of stamps that are not cancelled, she said "We can give you credit for damaged stamps, you know." 

"What is damaged stamp?" I asked. She paused a second and said, "Maybe I shouldn't be saying this, but those stamps you told me about, they could be redeemed

for new stamps."

Hmmmm....

You can not get new stamps for uncancelled stamps that have been mailed. they have been "used" to pay the postage on the item you received. they can not be "used" again.  If you accidentally stick a stamp on an envelope and then mess the envelope up, you can take the entire envelope in to the post office to show them it hasn't been mailed and most times you can get replacement postage for your "unused" stamps. Same thing if you mess up a book of stamps, If they were "unused" you can probably get them replaced. It is a big hassle to do it though, you have to fill out a refund form and find a clerk that knows how to put it in the computer.