Make sure it's nailed down as to what you're after.
Plenty of sparkies can and will do a great job with data.
More can do a great job, but will do an OK job because they don't carry the parts, don't want the hassle, and they bid for low cost. This is where you'll mostly find the plugs and the Cat5e.
Some just don't have a clue.
It's also worth noting that they do make fully certified plugs for solid cable that are reliable, e.g. this from Belden. But they're bulky and expensive. The manufacturers are saying people are starting to use them for things like IP cameras, WAPs etc. where the device is fixed and it doesn't really make sense to have a box and faceplate next to it or in the ceiling. You also see them used for industrial ethernet.
This is interesting product to know about.
We had a network installer come and do some repair work on the one above install. There are two cables terminated with site installed clear plastic RJ45 plugs going into the cabinet for exterior cameras. The installer didn't install the cables onto the patch panel, because there weren't any remaining ports on the patch panel. So there are RJ45 plugs on each end of the cable. After the network installer tested the previous installers work, he discovered that 1 out of the 4 RJ45 plugs was wiring incorrectly. The network guy said it was an easy mistake to make, because the wires can cross when they are installed. But it showed that the original installer didn't test their work.
I would also make sure they fully test the network with a continuity tester at each end of the plug, and also make sure thy label them all correctly. We still have one port on the patch panel, which is wired up, but where we don't know exactly where the other end of the cable goes.
Next time I am going to do much of it myself so I can then be sure it is all done properly.
Continuity testers are better than nothing. But for large numbers of outlets in commercial installations where you're aiming for the 20-30 year warranties, they want full compliance testing on every cable. For example, if the cable is kinked midway, or there's too much untwisted length causing crosstalk. This generally doesn't matter so much in domestic.