Can ISPs fake the results of internet speed test?

We moved to a new one he claimed to give us 15mb/s to 30mb/s and 30mb/s upload speed.

If you go to any speed testing site, like fast.com or speedtest.net or any other, you see that it shows 30mb/s and so on, so the numbers you see on screen back his claims. Ping is 15, so not a factor.

But if you download a big real file or app, you see that it gets downloaded at 200kb/s and the internet in the house slows down significantly.

How is this possible? I understand that he can cache Youtube and Netflix, but what I don't understand is how does cache has to do with the results from speed testing sites?

Solution 1:

It's definitely suspected that ISP's give priority to speed tests. There's not a great deal you can do about this except to try testing to a datacentre a long way from you, which may give a slightly different picture.

There are a huge number of factors that can make a real-world file transfer be slow, though. The far site's delivery capability, how busy it is between you & them, whether a CDN has it cached locally or you're having to fetch from half-way round the world… & that's before we get to your own local network - with bufferbloat, congested or noisy wifi etc etc.

To avoid the mainstream prioritised tests, I always give DSL Reports a try. I'n sure ISPs will prioritise them too, but they have additional tools you can employ if it detects some other factor in play.

Try https://www.dslreports.com/speedtest & let us know how you get on.
Also read their "Why is this the best speed test" section at the end.