Is it permissible for a Muslim to buy meat from shops owned by Arabs who have written on them "Halal meat," relying on the principle that the sin falls upon the seller and not upon the buyer?

There is no legal impediment for a Muslim to buy meat from the shops of People of the Book and Muslims, even if they do not state that it is halal, unless there is evidence or indications to the contrary. A Muslim should seek out what is permissible without extremism or undue hardship, for extending the blocking of means (sadd al-dhara'i') is not permissible if it leads to putting people in difficult situations. Therefore, one should not doubt the slaughtered animals and food of Muslims without clear evidence.