IMO it's not an unreasonable request but are you certain you want to return for exchange a tree that already has a somewhat natural bend already if your plan is to bonsai it ?

Now that I think about it I can see why your newly delivered tree would have that shops typical bend as they do keep them inside over winter nearly unattended at the south side full sun exposure side of there hot house.

Here are some pictures of the tree. As you can see, it is bent at the base of the trunk and will not stand up straight on its own. And yes I am planning on turning this into a bonsai but this is not the kind of bend I want my tree to have.

http://s1004.photobucket.com/albums/af165/mryan79266/

The tree's trunk seems rather straight to me. If you want it more vertical, just stake it to the vertical. My preference is always to have some movement in the trunk, so bending the tree in a lazy 'S' so the crown is eventually over the roots would make a much more attractive tree that has some personality - as opposed to something that will eventually probably end up looking like a lollipop. Your tree is commonly sold as a 'Bahama berry' bonsai starter. I've seen dozens of these trees in collections as small trees. Those with straight trunks usually appear too stiff & formal to be natural. Those with curved or slanted trunks look more natural & appealing to the eye.

If I was considering the purchase of that particular tree, my eye would tell me the feature least appealing is its trunk, because it's too straight. Fortunately, the tree is so young that can easily be solved by either wiring or pruning.

In the end, it's YOUR eye that determines what pleases you, but training the tree to vertical would only take about 5 minutes.

Al