We have the internet now. You can look up how to do these things.
But where do you get the knowledge to know that you picked the right guide off the Internet and that it isn't going to violate housing codes that don't exist in the area of the person who made the guide? Or how do you know that it isn't going to have a long term chemical reaction with the floorboards because the guy writing the guide didn't have such floorboards and didn't bother to mention the possibility? Or any of many things that could go wrong? You need knowledge in the first place in order to know which source has knowledge you can trust.
And regarding renting from the hardware store: it seems to work out fine for most people
I didn't even know that there is such a thing as renting from the hardware store.
I think you're being too risk averse here. How do you know you hired a competent person? Can you really be sure that they didn't do something stupid? Are you sure you won't need the money you spend on them for something else? Obviously you should do a cost benefit analysis, but in the cases I mentioned, the costs are way too high for basically no benefit besides saving a small amount of time.
Two of the main resources people have are time and money. The world offers many opportunities to trade one for the other, at widely varying rates.
Where do you see people trading money for time at unfavorable rates - spending too much money to save too little time? What things should people just DIY?
See also the flip-side of this post, "what are you surprised people don't just buy?"