No, the situation is different in Germany. You are not allowed to work under a visa waiver. The permit is something you personally apply for and not the company

No, the situation is different in Germany. You are not allowed to work under a visa waiver. The permit is something you personally apply for and not the company. Some time ago the permits regulating work and stay were unified so you only get issued one thing that contains everything. Some residence titles give you access to the whole labour market, some are coupled to a specific job, some don't allow you to work at all. There is a special exemption for US citizens (and some others) which allows them to apply for a residence permit after entering Germany on a waiver. Until it is granted, no work is allowed. The question though is whether "visiting clients" actually constitutes work. Just negotiating contracts does not, actually performing work there is (duh).