I have limited experience with it....I used to occasionally help a carpet layer buddy doing it. Ripping up old carpet, tack strip, etc. is easy....you can't really screw that up, too badly !
I installed that thin indoor/outdoor stuff in my basement easily and seamed it perfectly...that doesn't need a power stretcher or knee kicker.
An amateur won't have the tools or knowledge to DIY with a thicker carpet...esp. stuff like a seaming iron and all the other tools involved.
Carpet layers are renegades that work largely for cash under the table....sort of a no tax thing and the guys are of iffy character....most do take pride in their work. It requires skill to do it well, and the proper tools. Not a great DIY thing, IMO !
Easy to fuck this up with no experience !
Installation is not free. You are paying for it somewhere