I buy BTC/ETH in bulk, pay cash in Germany in the office at city center. 3-5% fee bitfinex-price. Buyer with reference.
Where is the reference? May we see it? Are they forum references?
Selling coins for cash to anyone who invites you to deal privately, even in a CBD or in Germany's
Finanzzentrum, is not always safe. Anything can happen. Cash must be checked very thoroughly. One reads of stories of traders getting assaulted and robbed.
There has to be a better and safer way of doing it. You might want to consider meeting up inside a bank but that too might not be enough. Why not buy from bitcoin.de or via SEPA on Localbitcoins?