Make sure it works first, then deliver judgment.
I sent a 200GB to Maxtor once - bad sectors. They sent me a 250GB. It also has bad sectors.
Next story:
I sent a 60GB 120GXP IBM to Hitachi - very nasty head crash. Got a 92GB 180GXP. It died less than 2 months later of the infamous IBM click of death.
Those were the only two times I've had replacements die on me though - I've done RMAs with Samsung, Seagate, and Western Digital, as well as one other one with Maxtor (this one was also for bad sectors), and the replacements all performed just fine.