Yanshang Teahouse is a store in Liyue Harbor, but cannot be accessed by the player.
Yangshang Teahouse apparently offers high-quality teas and "other goods", but they refuse to allow the common person to see what they have in stock. In order to enter, customers must pay a deposit up-front.
Sometime before the Traveler's arrival to Liyue, the previous owner had an outstanding debt for the Northland Bank, who in turn sent Childe and Javert to reclaim it by force. Childe easily overwhelmed and killed the owner and his guards, obtaining a Sigil of Permission in the process. He apparently spared Chuyi for reasons unknown.
The teahouse appears to have a notorious reputation, as Chuyi is extremely rude towards the Traveler for asking a simple question. Likewise, a notice on the Chihu Rock Bulletin Board states that she is a swindler who makes people spend all of their money.