Our pastor (sedevacantist) would typically take it case-by-case. If family members were present at the baptism and stated that the baptism was done properly, then our pastor would accept the baptism. If there was any doubt, he would repeat the sacrament.
Though the further we get away from the changes put in place by Vatican II, the more likely so-called Novus ordo clergy may introduce some kind of novelty into the process. So some traditional clergy are apparently repeating the sacrament more often as time goes on. It's kind of similar to what happened with the Old Catholic sect - for the first 50 years or so after they were excommunicated, their sacraments were still considered valid. But then so much time had passed and their training became questionable, so many clergy began not to trust their Sacraments any longer.