A quick look at the local buy and sell sites:
The HP 400FL listed for $75 that was bought from Value Village for $15 which my offer of $50 for was rejected on is still for sale. The pictures still show the $14.99 Value Village price tag on it.
The Agilent U1253B that I messaged twice and offered full asking price on but never heard back from the seller is still there. Several weeks later, I got a friend to offer full asking price and would've bought by proxy if it was me the seller had an issue with for some reason, but the friend never got a reply either. The 13 week old listing now has additional pictures though.
Beats me. The first seller would've been up $50 and the second $400 instead of $0 with their advertisements getting older and generating very little interest from other people, if any. I don't understand it.