When I saw you said etsy, I had to go look and sure enough you can get chaeto on etsy. Surprised the heck out of me.
I suppose it's like any other place.
Getting "clean" chaeto is kind of a catch phase IMO.
You get it, rinse it, inspect it, then use it.
Places like Algaebarn really depend on reputation. Any other vendors who sell it would have to hold high standards too.