Agree with Jason and Dan.
Jason made an great point on condition, postcard collectors aren't as concerned about condition and having a postcard graded by PSA or SGC is really a waste of $$$. If I buy a graded postcard I'll crack the slab and add the postcard to my collection. The grading companies don't understand the postcard collector and are really missing out on a huge (world wide) potential market for grading postcards if they were to do it correctly.