Are cheap relays dangerous?
What is the risk here?


This can be generalized into risk and cost. I find that in all my years of being a design engineer that the most cost effective and safe practice to adopt is this: -


Source parts from reputable dealers
Source parts that have reasonable data sheets
Use those parts within the constraints imposed by those data sheets
And more recently, only use parts that can be adequately modeled i.e. ensure there is a decent spice model available and use it (relays are usually exempt from this of course).


Following all the rules above ticks all the quality boxes for me but doesn't prevent me (or anyone) screwing up by being an idiot because that is human nature. However, it is about reducing risk.

Doing anything outside those rules usually bites you either by wasting your time (cost) or adding some form of risk to you or other people.

I've never sourced a component from ebay and I've never used a component that hasn't got a reliable source or a decent data sheet. In fact I've gone out of my way to use only components that do have decent data sheets. I'm involved with a project at the moment that is attempting to use a design made about 20 years ago and I just cannot use it because it doesn't tick all the boxes. I have to stand my ground because, at the end of the day, if we did use it, we would likely end up pissing customers off and damaging our reputation.