Can I eat at a restaurant if the worker says the food is Halal?
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The asl (principle) with regards to consumables is that they are Harām until proven to be Halāl.
Evidence giving genuine and credible conviction of a consumable being Halāl is necessary to move from the above quoted principle.
Merely having a flashing sign saying ‘Halāl’ is not sufficient. Likewise, merely for a worker to say the consumables are Halāl is not sufficient. Majority of the time, workers of franchises do not have any control of the ingredients used in the product and lack knowledge of how the products are processed. In such a scenario, one cannot rely merely on presumptions of the workers stating something to be Halāl. One must search for an authentic certification of the franchise or get written confirmation from the franchise owner of the processing and ingredients being Halāl.
However, if a restaurant or takeaway is owned by an upright Muslim who is well informed and acquainted with what is Halāl and Harām and is aware of the industry, giving you genuine and credible belief of the products being Halāl, then one may consume the products sold there.
If he is not trustworthy or he does not hold sufficient knowledge and information with respect to matters of Halāl and Harām, then one cannot consume the products sold there until and unless the store is certified by a reliable and genuine governing body or one conducts his own thorough research giving oneself a genuine belief that the products are Halāl.
And Allah Ta’ālā Knows Best
Mufti Faraz Adam al-Mahmudi,
Checked and approved by,
Mufti Husain Kadodia Sahib Hafidhahullah
 ” لبقائه ” أي اللحم على الحرمة أي التي هي الأصل إذ حل الأكل متوقف على تحقق الذكاة الشرعية وبتعارض الخبرين لم يتحقق الحل فبقيت الذبيحة على الحرمة (حاشية الطحطاوي على مراقي الفلاح شرح نور الإيضاح (ص 35 دار الكتب)