The fish that I have bought directly from hobbyist breeders have
never given me a problem.
If you buy from another hobbyist, you can discuss the TB problem and
evaluate their reaction. With all the current TB problems, any
serious breeder should be protecting his breeding stock AND his
reputation.
Last year I had two shipments of Rainbowfish that I believe were NOT
carrying disease. One was from AquaBid (Tanner, LAX guy) and the
other was from WetThumb Aquatics. This is just a single
experience. However, Rainbowfish breeders that sell directly to
hobbyists have a powerful incentive to keep their stocks clean and
sell healthy fish.
As to eggs, yes, one must consider that the mop could be carrying the
bacteria. But again, you're buying directly from the breeder,
thereby, decreasing the risk of bringing Mycobacterium marinum into
your tanks.
I don't think there are any guarantees in buying disease-free fish.
However, you can minimize the risk by being aware of the M. marinum
problem and taking commen-sense precautions.
I have learned a lot from all your comments. It's been very helpful
to me.