Not really working for me. Life at PSB is so slow , I tried to order a bunch of WL books from the marketplace  . Not happening, No shipping discount  for multiple books, $3.99 per book. Really!!! Exited and ordered from Amazon. Is this suppose to be a charity!!! 

No, it's not supposed to be a charity.  It's a business, as you have pointed out many times before.  PBS sells books, just like Amazon and B&N and Thriftbooks, etc.  They charge shipping, just like all those other places typically do.

You CAN get shipping discounts if all of the books you order are at the same warehouse.  But I've found that to be rarely the case.

I find the prices in the PBS marketplace to be great. I always order the overstock books, however, so the shipping is 3.99 for the first book and .99 for each additional one. I have found it to be well worth it.

Yes, there are multiple item shipping discounts if the books are being shipped from the same location. But there are a few different suppliers so not every book comes from the same place.

In my experience, PBS Marketplace seems best for pretty new but not brand new books - stuff that's probably still wishlisted on PBS but not something that just came out. The prices are decent but not astonishingly low. For anything that's been out more than a few years, or that would have had a lot of copies printed when it first came out, like bestselling fiction, you can probably find a better deal on Amazon, ebay, half.com, abebooks, etc.

I only buy from the marketplace when I am willing to spend some of my PBS credits to lower the prices; otherwise other vendors are competitive price-wise and much quicker to ship.