Your real issue is foul brood...
If you wash it VERY well after it is returned you probably will be without issue.
If you feed extracted honey to your bees, my concern would be increased.
If not, its not likely to be a problem (as long as you clean it well).
In fact, I'd tell him/her to clean it first, and then I'd re-clean it again.
Foul brood disease presents itself when enough infectious spores are present.
By cleaning you decrease the amount of spores and viability of the spores that are present.
I don't lend any of my extractors out.
Anyone that looks long enough can find an old hand crank one for a few bucks at a garage sale or such.
In the past I have gotten one free and another under $20.