How can a buyer verify hit likelihood in a repack break?

Ask whether the odds were locked before the break and timestamped. BreakersDNA calculates hit likelihood from a certified manifest and locks it before the first pack opens, so the figure on screen provably did not change once cards started appearing.

An odds figure that can be revised after the fact is not an odds figure. Locking and timestamping matters as much for the honest breaker as for the buyer: it means the numbers shown on stream cannot be second-guessed afterwards, because the record proves they were the same before and after the pull.