The grout manufacturer says it is unnecessary to seal and is extremely stain resistant. However, if these jobs were going in our family's homes, we would tell them to seal it every 6 months or so with any generic grout or stone sealer.  We would also recommend they use a ph neutral cleaner intended for stone and grout, even though many more options would work fine.  We have tested Windex, Dawn, and even Chlorox bleach without any obvious negative reactions.