Sheikh `Abd al-Wahhâb al-Turayrî, former professor at al-Imâm University in Riyadh
It seems to us – and Allah knows best – that participation in an open buffet is permissible.
It is true that in Islamic commercial law, contractual uncertainty (gharar) can lead to a contract being deemed invalid or unlawful. This is the case when the degree of contractual uncertainty is major or unjustifiable.
The degree of contractual uncertainty in the case of an open buffet is not something major and will not affect its essential permissibility. It is an established principle in Islamic commercial law that if the uncertainty involved is something trivial, it is to be tolerated and overlooked.
The amount of food taken by people, in most cases, is roughly equivalent.
Nothing in Islamic commercial law appears to forbid such a practice.
And Allah knows best.
Source: Islam Today