Not everybody considers their ducks to be pets. Mine are LIVESTOCK. If this person is investing money to make money, there is nothing wrong with that. Investing in a breeding pair right before breeding season starts up (admittedly I don't know anything about mandarins, or when their breeding season IS, how long, how many clutches etc), seems like a good way to possibly make money off of your stock. Get a pair for 50-75.00, and sell ducklings for 10.00 apeice (once again showing my ignorace at the 'going prices' of mandarins - this is just an estimate as I've never shopped around), and you'd need to sell a clutch to make back your initial investment. Not too bad of an idea. They're also small so they wouldn't eat you out of house and home, either. If you get multiple clutches per year out of the birds, then I think you could make money selling them. That is, if the market has the demand.
This is all based on the idea that this person has adequate food, housing, pen space and can indeed adequately care for the necessities in the birds lives. And, of course, that they can spare the investment price without themselves, their family, or their other animals suffering.