I had this same problem on many of the items I purchased (and some that were free).
Sometimes items you purchase have other content with them that you aren't aware of.
The physics football players contained the "buzzcut" hairstyle. Because I had not purchased that hairstyle, the avatar would load with the trial watermark. The free John Connor character had the same problem.
When you load an item you paid for in the MP. Make sure you are connected to the Internet the first time you load the new content. If the watermark is still active, on the project tab, right panel, select "buy trial content" button. This automatically identifies what content is showing as "trial" (I.e. hair or clothing) and takes you to the product page for that specific content. At this point, you can choose to purchase that content or simply remove that specific item from your scene. If you replace the trial cloth or hair with something you have that isn't trial content. The watermark will go away, leaving the item you actually paid for without the trial watermark.