Question

What did Muslim merchants do in order to make trade exchanges less problematic?
Fed and entertained their trading partners.
Established a system of tariffs.
Wrote down the exchange rates for various items of trade.
Standardized weights and measures.

Answer 1

Well, i think the answer would be : Standardized weight and measures

Standardized weight and measures first developed by the muslim merchants in Cairo. Before this standard, Length was measured by the length of one's body. 

For example to measure silk, the usually used the term such as 1 arm length.

The thing is, many traders started to hire shorter people to measure this to gain profit , making exchange often became problematic

hope this helps