Chili777 said:
For me, the two most important traits in a vendor are honesty and communication. Not every one of them manages to meet that bar.
Testing should be paid for by the vendor, and I need to be sure the COAs they show are up to date for whatever I'm buying. Every vendor I use has built a solid reputation among their own buyers, and that reputation is part of why I stay.
Once a shipment goes out, I expect the tracking number to come to me without me having to chase it down.
There should also be some way to follow the order and find out if something goes wrong. If the vendor spots a problem, I want to hear about it from them. A couple of my vendors will actually message buyers along the lines of, "This is stuck in Customs and we'll order a reship by the end of the week, if the status is the same". That's good service.
Standing behind the product matters too. My main vendors will swap out anything that doesn't live up to the quality stated on their COAs. The better ones will do that when a buying group hands them a Jano COA as proof.
A vendor can vanish overnight, but while they're operating, these are the things I look for.