Tourists (and locals) cannot purchase Cannabis products containing THC in Germany, and this may not change. You can not lawfully acknowledge weed from a German local who has been growing it for their private use in the home. This could criminalize you and him. I.e., your Airbnb host is https://arthuridsgu.pointblog.net/5-easy-facts-about-buy-cannabis-in-germany-described-82461874