Hi, question: (1) Was the following a valid contract? and (2) was an offer made, or was this an invitation to treat?

"M" puts up an offer on amazon to sell a product for $12000, self collection.

"N" was interested and facebook message: Is $10000 ok?

"M" replied that someone else had offered $11000.

"N" in return offered $11,500 can to self-collection the following day afternoon.

"M" replied: "Yes, Ok! Please transfer $500 deposit today and pay the rest tomorrow". and then provided mobile phone no and home address to "N".

"M" then realised that evening that his own friend needed that product for personal use. "M" reached back to "N", transferred back the $500 deposit and said that "sorry, I won't be selling the product anymore. I have transferred you".

"N" was shocked and replied that "I thought we had a but bidding deal?". "M" replied "No, I don't think so"

I have to base my answer on the 4 elements of contract: offer, acceptance, consideration and intention to create legal relation (no in this case, as "M" and "N" were friends").