Of course there's always that chance, but trust is a two way street. They trust you enough to send you money and ingest your homemade drugs, but you don't trust them to test your homemade drugs?
If you had testing for everything that you sell you would have a counter argument for such a situation.
Should that ever happen it would be easy enough to ask another one of your happy customers to send theirs in. On top of that, we aren't stupid here... Well, most of us anyway. When some little fuck with one post crawls out from underneath his rock to post questionable results and talk shit, we tend to get a little skeptical of their claims.
With that said, do you require buyers to state up front that they plan to test your tablets? Also paging
@janoshik at any time do you ever catalog the samples you receive with photographs?