@divinitty He should be given a compensation of a free refund for 50% of the value of this refund. You should make it clear to your customers that phones can get locked. The customer has no reason to ask this on their own as they are unaware of the possibilities. But you are not.
This compensation should cover any potential losses as the phones can be bypassed (by bypassing the blacklist) but will probably be sold for less than the normal resale price for them as they are going to get blacklisted as soon as they are on.