Have purchased perhaps 100 tubes for my two tube pre-amps and two tube power amps during the last 18 months. Purpose is to inventory a stockpile good til I die since the price of NOS keeps climbing. Of these, three (3) were noisy with crackling, creaking, or microphonics. I feel the only arguement acceptable for “breaking in” tubes is to allow them to mature to sound better. It seems like the seller may be hedging that replacements from his shop could repeat the problem. Flag. If they are cracking/creeking out of the blocks I would consider that a defective tube or indicative an inferior manufacturing process. In my case, sent them back for a refund and moved on. Its good your seller offered up front to accept a return. Good suggestions in previous responses where to find reliable tubes.