"make an offer" posting -- what are rules with multiple offers?

[crs_crs1]

I recently made an offer on a listing with a "make an offer" option. The item sold for the full "buy it now" price about 8 hours later the same day. I got the "offer rejected" email after the winning big was accepted. Given the time lag from my offer and the timing of the winning bid, I wonder if the seller used my offer to get a full price bid from the 2nd person. I would have paid the full price had I been given the choice by the seller. My question: If 2 buyers make the same "make an offer" offer, is the seller obligated to make a counteroffer to both? And does the 1st buyer get 1st crack at buying?