My first job out of college we made our own patch cables. Usually we'd make them "on demand" as needed for a new server or workstation. My (then) boss didn't want to buy patch cables even though we knew that we weren't doing a perfect job (we were software people, eh?). Any time we had a flaky server problem it would turn out to be the cable... usually one made by my (then) boss. When he left the company the first policy change we made was to start buying pre-made cables.
That was during the days of Category 3 cables. You can make a Category 3 cable by hand without much skill. With Category 5 and 6 the tolerances are so tight that just unwinding a pair too far (for example, to make it easier to crimp) will result in enough interference that you'll see errors. It isn't just "having the right tools". An Ohm Meter isn't the right testing tool. You need to do a series of tests that are well beyond simple electrical connectivity.
That's why it is so important to make sure the cables are certified. It isn't enough to use the right parts, you need to test it to verify that it will really work. There are people that will install cable in your walls and not do certification. Some will tell you they certified it but they really just plug a computer at each end; that's not good enough. I found the best way to know the certification was really done is have them produce a book of printouts, one from each cable analysis. Put it in the contract: No book, no payment. (and as a fun trick... the next time you do have a flaky network connection, check the book and often you'll find it just barely passed. You might not know how to read the graph, but you'll see the line dip closer to the "pass" line than on the other graphs.)
If your boss isn't convinced, do the math. Calculate how much you are paid in 10 minutes and compare that to the price of the pre-made cable.