If I may interfere here,
I think you guys are taking advantage of MintTea here.
Muffy is a tier 2 villager and is in pretty high demand right now...
600k is WAY bellow her current value.
Mint, I believe you could sell her for about 3 mil or more,
but it is your choice.
It is true that you said you were selling her and gave an initial price of 600k.
While it's an innocent mistake other users are in right to claim her for that price.
I suggest you label this thread as an auction, that will limit the confusion and unhappyness of buyers,
as the villager will go to highest bid.

If you want to limit the price just set a minimum bid and a buyout price for which the person will automatically get the villager.
I also suggest you set a time for the end of the auction.
Since you are new I'm sure everyone will understand and no grudges wil be held.
It's only normal that you get the worth of what you are selling.