Sweat of a kaafir

Q: I read that the sweat of a kaafir is impure. In the Uk there are lots of shopping centres where the cashiers are non Muslims. If we go to the cashier with our food or clothes and they touch it to scan it are we not allowed to wear those clothes and eat that food?

Binaa

Q: What is the procedure of doing binaa in salaat? Do you have to go back to the same place in Haram or is it ok to read from anywhere in the Haram once you have redone your wudhu.

And how do you rejoin the salat, in which rakaat etc in the situation where the imam has already finished?