It's not Yelp who is charging them. They have a pre-existing business relation with Grubhub that generates leads for them for a fee, and, according to Yelp, al

It's not Yelp who is charging them. They have a pre-existing business relation with Grubhub that generates leads for them for a fee, and, according to Yelp, allows Grubhub to charge them for any lead generated on any partner platform, which Yelp became in 2018. So now what used to be a free stream of customers is hijacked by Grubhub. I'm sure it hasn't crossed their minds when they signed up with Grubhub that in addition to new sales generated with them, they will also start paying commission on their existing clientele. A business owner trapped in a market where the Grubhub-Yelp duopoly is proeminent is basically fucked, and they will use their rent seeking revenues to further entrench their dominance by offering consumer discounts, fidelity options etc.