Blatant shill bidding I believe
I agree with a shill bidder. If so, seller Bigdeezguns just paid a hefty GunBroker fee for having his Bro-n-law bid at the last moment to see if they couldn't squeak out a few more dollars on a legit bidder. Yes, lets watch out for this one to reappear in the next few weeks...
I only know of this because I bought an item one time that the Seller messed up on the price (nib SP5K and had it listed $1k under fmv). I thought I scored big time. He contacted me within 5mins to explain he entered the wrong price and could not honor the sale and would understand if I gave him an F rating. I understood and let it go. A few days later I got the email of no-sale and did not dispute it. In my case it was just an innocent typing error, but I think this is how a shill Seller must be circumventing the Seller fee.