I would think nothing of it - it's none of my 
business.  How would I even know you did do this 
unless you let me know as you were doing it?  
Besides, if it was good or bad, person A would 
certainly let you know wouldn't they?

^_^  Just out of curiosity, why would you (the 
hypothetical you, that is) do such a thing?

That's just me, though . . . ^_~  My own 
hypothesis - If I knew you and you decided to 
sell the gift, I probably still wouldn't say 
anything even if I thought it was non-ethical.  
That's your choice.