Since all exchanges in a market economy are voluntary, how do we know that the exchanges will probably benefit all participants

It depends if what you have in exchange is a commodity or product that other party wants and is in need of.  If they are satisfied with what they have received during the exchange and you are satisfied with what you received in return then that means that the exchange was beneficial to both parties.

for many centuries there were important factors which the economies of the muslim empires developed increasingly. they applied economic procedures in production, investment, finance, taxation and property. they used to tax certain goods (for example: harvest), they charged interest on money lent, they signed contracts with merchants; they relied on a common currency, and they used checks as well as promissory notes. with the money collected by means of taxation, the government provided the needy with an income. in addition, trading networks covered huge distances, so far regions started to have contact and exchange goods. this trade network covered areas of asia, africa and europe.