Will I be liable if I sign an offer letter and take another better offer later?

Dear client,

The job offer letter is not binding in nature. If you are getting a better offer, you can think of a second option as well.

Thanks and Regards

Yes, but if they made a visa or any procedures, they have the right to refer to you for compensation.

It is preferable for you to postpone signing until your position is stated with the second company.