Imo all sources should come with testing results. If a source is not going to invest in their own business why should anyone else.
While not as good as having members test Vials it at least shows that you have confidence in your product and are in it for the long haul.
It may take a cost at the beginning to have testing but if you have a quality product and turn out to be a good source you will more than make that money up on the back end. Coming with testing shows that you are serious about this.
As
@BigBaldBeardGuy has already stated,
for me the main things I would want in a source are
1. Product Quality/Testing
2. Sterility (Lab setup and products)
3. Safety/OPSEC
4.T/A + Communication and Customer Service