Is Memtest86 reliable?

Hello, new forum member here, looking for a little info/help.

After getting many BSoD since I bought my PC, I was advised to run Memtest86.

The actual test (4 passes) was successful with no errors, but it reads one of my 4 RAM sticks as 2133 instead of 3000.

I spoke to the vendor of the PC, who told me they won't help as my CPU is only rated to 2133, and won't honour the guarantee because of this. I am confused about this as I bought a complete system from them.

I wanted to swap the order of the sticks, so I could see if the issue follows stick 3, or remains on slot 3 of the MOBO, but am worried the vendor would say this invalidates my guarantee, as I would have to remove the cooler and am not familiar with re-fitting one.

I was hoping to find out if this problem with one stick not running at the right speed is common, or if there are further tests I can do without changing hardware?

Thanks in advance for any advice!

A really good way to get memory or CPU errors to crop up is to use Prime95. I was having BSoDs that I couldn't figure out, and Microsoft Memtest and Memtest86 both reported no issues. Running Prime95 showed me failures within seconds.

Turns out that the power controller on my motherboard was supplying my RAM with a little less power than it should have been getting. I upped it by .1 volts and not a BSoD since!