I work as a bike mechanic at one of the largest Specialized dealers in the US. A couple of times a week we have people that come in with bikes they bought from

I work as a bike mechanic at one of the largest Specialized dealers in the US. A couple of times a week we have people that come in with bikes they bought from direct to consumer brands and attempted to assemble themselves. People regularly make serious errors when they assemble a bike themselves, and they're often dangerous and sometimes expensive to fix. Unless you're 100% confident in your bike mechanic skills, you'll likely spend all of the money you save buying online at your local bike shop to have them fix your own mistakes.