You did not exactly specify what you were confused about in one of the sentences in TOEFL's written expression, but I'm guessing it's the use of the unreal conditional structure - "if it (or they) were to allow unrestricted use of detector, many antiquities would be stolen." - am I right?
The unreal conditional structure is used when one talks about unlikely conditions in the present. For example, "If I enjoyed games, I would buy a Games Master."
(But I don't enjoy them. So, I haven't bought a Games Master.)
"If Sherwin didn't like his job, he would look for another one."
(But he likes his job. So, he doesn't look for another one.)
"If I were a bird, I would fly to London."
(But I'm not a bird, so I can't fly to London."
The speaker talks about conditions in the present, but uses words that are in the past tense. This is the unreal conditional structure or second conditional sentence
I hope I've helped you somehow.