The following witnesses are posul [invalid]; a gambler, a userer, one who sells the fruit of shmitta, and slaves. In any case that a lady is not kosher, these are also considered not kosher.

Rosh Hashana 1:9

If a witness saw the new moon but is too weak to go by himself on Shabbos, his is put on a donkey or a bed. If he is afraid of an ambush, we send along people with sticks. If it is a long way to go to bais din, we send along some food.