Adsense works because you trust google and google constantly “checks results” - it moderates ads, runs fraud detection, bans bots and scrapers from google search etc etc etc. so basically its googles killer feature how to check the results and its closed sourced
It can be called performance metrics too, yes, but those metrics should be evaluated by one who receives sats imo. Or do you think its just a payer who has to validate results and decide if they want to continue working or better find another service provider?
If its upto payer then how you protect from the basic form of fraud like “saying I finished work for every incoming task”? You want to assign scores using web of trust and limit the usage of your app to those who have rating above X?