Zachary M. Seward, Quartz:
The size of GrubHub’s cut varies depending on how much the restaurant is promoted. The prospectus explains, “Restaurants can choose their level of commission rate, at or above the company’s base rates, to affect their relative priority in its sorting algorithms, with restaurants paying higher commission rates generally appearing higher in the search order than restaurants paying lower commission rates.”
Or, as we common folk call it, “bribery”.
Kidding aside, no matter how dirty this feels (and, boy, does it ever feel dirty) this is pretty standard. Looking at reviews or star ratings may not necessarily be good indicators, either, as those who wish to vocalize their complaints tend to dominate reviews. Word of mouth and recommendations from your friends are still your best bet.