Are buffets allowed?

Sheikh 'Uthaymeen raḥimahullāh said regarding food outlets that say: 'Pay twenty riyals and eat until you are full?' الظاهر أن هذا يتسامح فيه؛ لأن الوجبة معروفة، وهذا مما تتسامح فيه العادة، ولكن لو عرف الإنسان من نفسه أنه أكول فيجب أن يشترط على صاحب المطعم؛ لأن الناس يختلفون. "What's apparent is that this (gharar - uncertainty/risk) is overlooked because the [size of a] meal is known, and this (risk factor) is something usually tolerable. However, if a person knows within themselves that they eat a lot, then it is necessary to stipulate with the restaurant owner because people differ." [Ash-Sharḥ Al-Mumti' (4/322)]