Why not just accept the gift and then return it yourself rather than ask that person to?
I learned this at a young age.
My sister bought me a Quiet Riot record for Christmas...being like 8 or 9 at the time I stupidly said "Thanks for the album but next time I prefer tapes."
Remember the old saying that it's the thought that counts? It was awesome that my sister bought me a record. I erased all that the second I made my stupid comment. I could see it on her face.
Nowadays I would accept the gift and then go exchange it for a "tape" etc. ya' know what I'm saying? Of course we now have a rule in my family that gifts have to be edible or drinkable (preferably alcohol) and consumed with the person who gives the gift. :glugglug:
While your desire for your mom to "get her money back" definitely shows integrity, you could still hurt her feelings by asking her to return it. You have to decide if it is worth that. If you want a PS3, I say return the Wii yourself and exchange it for a PS3...
OR, go search Youtube for "hot chicks on Wii" and you may change your mind and keep it.