Married men can actually be best men, there is no taboo to say.
In the folk custom, the best man can only be unmarried single men, married or divorced men can not be the best man, but in fact, there is no basis for this, at most can only be a traditional custom. When considering whether he is suitable to be a best man, it is necessary to consider factors such as his character, relationship with the groom, and schedule, rather than whether he has been married.
The best man is the groom's personal butler role at the wedding, from helping the groom to marry the bride smoothly when the door is blocked, to helping the groom block the wine during the dinner toast, every link requires the best man to do his duty, so there are many requirements to consider when selecting the best man. It would be a shame if a man who is qualified for the best man job in every way was passed over just because he was married.
Folk believe that married men when the best man is a big taboo, mainly that married men have used up their good luck in marriage and love, and will no longer have any blessing role for the couple, but this kind of argument has no basis for support, and is not recommended as the standard for the selection of the best man for the new couple.