I have missed several... some cause I was cheap and some cause I was slow. I even torture myself every so often by looking at completed GB auctions and seeing the Buy it Nows someone jumped on before I saw them. Two that stand out occured in the whirlwind that is pre-wedding mindset.

1.) A month before I got married my future father-in-law took me to a big flea market looking for treasures. We parked the truck and within 60 FEET of the truck there was a table with a Baker Gun Co. 32 in Krupp steel, Highly relief engraved...quail in ovals akin to a Smith grade 5, including large amount of additional scroll. Only issue was a 12 in LOP and no buttplate. $400, seller ready to deal... he suggested $350 as I walked away. I didn't want to look like a lunatic to my new FIL throwing hundreds at the first thing I saw. Went back 30 minutes later and it was gone.
2.) the week before my wedding a "neat" Ithaca Flues Grade 6 went on Gunbroker right around $2500. I was the under-bidder and chickened out on going higher. No guarantee it was gonna stay "cheap" but I would have loved to get it for what the buyer got it for!