How do you prevent this?

Thinking of taking my 'home' business and going to some expo's. What are some ways to prevent theft? I was at an expo yesterday and there were booths with expensive items and they had purchased two sections and had 1 person sitting to take money way back in the left corner- and they had isles of products like a store- when i saw their set-up i thought omg- they have all of this product "in the dark".. i bet so many people steal from them.... So it got me thinking- what are the best ways to prevent theft/ deter someone from stealing from you?