It is said that you have to listen and believe in what a Muslim say to you, because if he is lying then he has to answer to Allah about it. If he says say he “dont know” then better not to buy it.
I know many people lie now a days but you have to track yourself accordingly as its said in Islam.
If you still doubt then dont buy it. or if you doubt that a cooked food is even not halal dont eat it.
If you want to make one thing Surah Bakrah then you will make Islam yourself complicated.