The type of router they are using — in most cases, the one supplied by their provider is often flaky — also contributes to poor transmission. Finally, the type of building they live in and the presence of other devices that transmit signals could also be sources of interference.
The best way out, as I have found, is to avoid wireless and use Ethernet instead. I initially tried out a number of wireless range extenders and while these worked for a short period, they became ineffective thereafter.
After some years of trying, I gave up and decided to get some Ethernet ports put in. To a large extent, this was done because my son would often come to me and say, "Dad, the Internet is slow. Can you speed it up?"
When the second also made an offer in the thousands, I asked him whether he was catering to home connections or only to businesses. He was somewhat offended at this and told me that his charges - $180 for a callout and $90 per hour of work (his estimate was that it would take at least 10 hours) - were reasonable.
The third guy was more down to earth. When I told him my requirements - five ports - he said it would cost $100 per port. Needless to say, he got the job.
On the appointed day, two young men turned up at my house early in the morning. Seven hours later, they were done. There were some minor changes: I had decided to put in only four ports. And the guys found putting in one of the ports more troublesome than the rest as the room in question has no ceiling.
So they charged me $150 for that room. All in all, $450 for the job was very reasonable. They used industrial quality cables for the job and I only had to provide a switch so they could piggyback off my router.
Now slow speeds due to wireless snafus are no longer an issue. Only when I use my mobile is speed an issue - but one can always switch to mobile data and get around it.
I have a hunch that if I had bought a more expensive router - the one my provider gave me as part of the plan is a very cheap one - that would have done the job as well but I just couldn't be bothered. It would have cost about the same, though.