I know of a few ways they can do it.
so to everyone here that is renting from NH / WH consider that
f2pool can send dead hashers to WH/NH with ease
Can you explain what you mean by "send[ing] dead hashers?"
When you pay for miners at *Hash - you have no idea what the miners are and what they are doing.
*Hash don't care either coz they get paid BEFORE you mine and they wont lose anything.
The people who own the miners will get paid no matter what also.
Thus someone could provide "bad hash power" on *Hash and no one would know unless they mined a VERY large amount and kept track of the statistics ... ... ...
Even if you did mine a very large amount and keep stats, there's no way to tell which miners of the ones in your order are the bad actors. Miners connect/drop/reconnect to your order based on whatever algorithms *hash uses, and by the settings the hardware owners configure.
Basically, as a renter you can absolutely never make an informed decision about whether the hashing power you're renting is behaving badly.