thing is it's the buyers perspective. it's what people see when they look at that ad.
for example i'll walk you through my thought process as i look at that ad:
it's an evo, a gun that is known to be a pretty high standard out of the box and in a lot of cases people who attempt to "upgrade" the base tend to end up making it a lot worse.
so the first question is what bits are in it? are they better than standard? well i don't know because it doesnt say in the ad.
the next question is have the parts been assembled correctly? well that comes down to the skill of the tech, as there's no big name drop of a professional tech (eg if you'd paid someone like negative airsoft or the like to do the work) then the assumption is that you've done the work yourself.
so how can i assess your personal competence as a tech? well i haven't got much to go on as i don't know you personally or your reputation. so the only thing i can really go on is the ad itself.
of course as i mentioned, if the effort hasn't been put into the ad then it begs the question has the effort been put into the gun? and with a lack of information it's just human nature to assume the worst.
this isn't meant to be insulting btw, this is meant to be constructive criticism, to point out where people who might otherwise be very interested in buying might change their minds and decide that maybe grabbing a brand new gun that comes with a warranty and they know will perform to a given standard is the safer option.