That's the kind of advice that authors write when they're tailoring an article towards an audience that wants/needs to read about that topic.
The assumption is the buyer has no idea what they're getting themselves into which is fairly opposite of the average member on this site, and it's very easy to be conservative and suggest someone else put more work into something rather than less then have them angry that "if only I had been told (something)". Authors are also trying to generate content in general, especially on paid articles they can go on and on about best practices and obvious information just to Fill A Page With Words And Get Paid Doing It.
On the other hand you can read independent shop reviews to weed some out, then call a few to find out what it would take to get an inspection done on the spot and the price, as well as inquiring whether anyone very familiar with the specific vehicle is available to do that. Maybe there aren't any in your area. Maybe you just didn't try hard enough to find them. There are more independent shops out there than you might realize until you start looking for them. Granted it used to be that even many gas stations had competent mechanics and a bay or two but not so much these days. Anyway good advice as already given to draw up a contract that stipulates a refundable deposit will hold the vehicle till it can be inspected. A reasonable seller should agree to that unless they're getting flooded with offers and want the fastest sale but if getting flooded, the price may be suspiciously low and the vehicle is that much more likely to have a problem. If anything most people tend to OVER value their vehicle, not under value it... guess that depends a bit on what it is too.
Depending on how much you want to spend, one thing about the shop that you can't so easily DIY is in depth testing. Suppose you want a compression test done, well if I'm selling a vehicle there's no way I'm letting a prospective buyer pull my spark plugs and do that, but if a shop is being paid and they're insured against damages, and I also have more presumption that a pro mechanic knows [censored] they're doing to reduce the chance of damage, I'm going to agree to it if they even mention it's one of the tests the shop is doing which they probably won't.
There is also the assumption that if you are reading a general advice article that you're spending more for a vehicle because this reduces the chances of repair work needed, so you're safeguarding against a larger loss of value than on a $2K beater, and the more a vehicle costs, the more time you tend to have before it sells unless it's priced very low and then that should be a red flag, anybody today knows you can get a car's value on the internet.
On the other hand you might find some cherry, something garage kept in near perfect condition, usually owned by an older person who has all maintenance records. I feel it's a lot less likely this will need a pro inspection done if you don't find any funny engine noises or tranny shifting problems and do a rust and leak inspection yourself. You do absolutely have to lift or jack or ramp up the vehicle to get under there enough to do a thorough rust inspection but on certain vehicles you can check the most common problem areas first like around the wheel wells where the wheels throw up road muck, especially near strut tower mounts on unibody vehicles as that's a serious safety issue, and along the rocker panels.