They tried this with me once. I told him to get a modem from the truck and try it. The issue remained, so the excuse was busted.

That said, I have run into issues where the ISP will upgrade the speeds and it will be beyond what the modem or router can handle, and as a result the speeds dropped dramatically. In those cases, I did need to hardware, but was still able to get my own.

You have to be careful with that too. I had a tech come out to fix what ultimately ended up being a faulty ONT and doing the same thing, hooking his test modem up to the line to make sure it wasn't my router causing the packet loss. Next month my bill was double because Verizon claimed I had a second line attached, apparently the tech's router registered as a second device. Thankfully tech support was able to reverse that charge, but it was annoying.