Might be worth you internally marking your repaired items after this, just to ensure that what does get returned to you from these sort of ‘clients’ is actually the item you sent in the first place!
I will be able to tell immediately on any item ive repaired anyway I recon, I can tell if something is something I have repaired or not 9 times out of 10, just by the solder i use, how it looks and my normal tell tales
. I seem to always rememer a device ive seen before. I've re-repaired a few things over the years. I think a couple of switches have come back like a year and a half later with a totally different fault and I'm always like "yea I remember that port, looks nice" 
