The amateurs usually run benchmarks (because they can't reason about it as they lack the relevant knowledge) and believe they got a useful result on some aspect when in the fact the benchmark usually depends on other arbitrary random factors (e.g. maybe they think they are measuring FMA throughput, but are in fact measuring whether the compiler autovectorizes or whether it fuses multiply and adds automatically).

A pro would generally only run benchmarks if it's the only way to find out (or if it's easy), but isn't going to trust it unless there's a good explanation for the effects, or unless they actually just want to compare two very specific configurations rather than coming up with a general finding.