For any sales calls, meeting, business contacts I would recommend to use "Hochdeutsch" but don't be shy to show a personal accent.
Only place a dialect really fits into a business talk: if you live/work in the same region as your business partner and only if they use dialect. In that case the dialect could be used a local identifier.
E.g.: I'm Austrian and live in North Rhine-Westphalia - whenever I talk to Austrians my accent comes out a little bit stronger - But even when talking to Austrian client/business partners I try to speek Hochdeutsch - not the regional Austrian Dialect (which are all familiar to me)