Agree. The "serious buyer" logic is kind of weird.
People who tested amps but ended up not buying are usually as follows:
(i) the amp sucks.
(ii) the amp does not meet their expectations or tonal needs.
(iii) they like the amp, but need to shop around a while before deciding.
(iv) they like the amp, but need time to assure if they "really need it" to avoid buyer's remorse.
(v) they like the amp, but need some time to raise funds before buying.
(vi) they like the amp, but need to "research" the specs, prices, opinions and functionality before deciding.
(vii) genuine time wasters who test amps for kicks
Category (i) to (vi) are actually "serious buyers" to varying degrees. As the amps cost hundreds to thousands of dollars, people do need time to decide, depending how deep their pocket is. IMO, the $5 fee will end up alienating many serious buyers because people don't like to have their "arms twisted". Just a thought.