39 karma · joined December 11, 2015
Your analogy with mystery shopper doesn't hold the water as well since the researchers in such cases are just executing the primary function of the businesses in question. So while for the bigger sites you might be correct that the research is not a human subject research but it's still an abuse of service which in unethical without consent as well.
I'd say all the services which require face to face interaction will become way more costly if such buffers will be needed to cover off hours. For example: there is a notion of skeleton crew and the service might not be operational without that crew so the choice is actually to spread the cost of off hours low load to the high load hours or close the business for low load hours.