السلام عليكم و رحمة الله و بركاتهIs there a phrase you say to the seller so that you can be saved from being cheated?? Should i say it in Arabic to a non-Arabic speaker or should i say it in his language since he does not know arabic??

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

You may condition on the seller to have the choice, such as saying to the seller: “I have the choice for three days”, for example. If you condition to have the choice on the seller and he accepted it, then you have the right to keep the commodity if you are satisfied with it, and if you are not satisfied with it, or that you find that it is deficient or that you are deceived with it, then you may take it back to the owner during the time of choice.

Ibn Abdul-Bar said in at-Tamheed:

"If a man conditions on the seller that he has the choice for three days about what he bought from him, and said to him: “If you cheated me in this commodity and your deceit becomes evident in it, then I have the choice for three days: if you wish you may keep the commodity and if you wish you may return it to him, then he has the right to this condition, and this is permissible, and he has the choice according to his condition.”

However, you should condition this with what the seller understands, like with his own language or by a sign that he understands so that the purpose is achieved, and so that there would be no disputes.

Al-Madkhal fi Usool al-Fiqh (the introduction to the fundamentals of jurisprudence) about the terms of the contract, reads: "...that each of the parties of the contract should know what was issued by the other party, like listening to his words, or reading what he had written and understanding it, or seeing his action or his indication and knowing his intention from it. If there is a breach in this, then the contract is not concluded. It is as if a person says something that indicates acceptance and the other answered him in a language that he does not understand…..”

Allah knows best.