outside of the tavern there is a weapons dealer. He is right across the street from the tavern going towards the world map. he will be there the whole game. If you need extra money use the same import tricks to get weapons to sell for cash. save game, drop all valuables the import the save person and pick up the weapons and sell them.

also, you can't sell weapons until you get to Baldur's gate, the first 5 or 6 levels (probably 2 or 3 hours of game play) you have to play through to get to Baldur's Gate, and there's no buying and selling in the beginning of the game.

where do you find the secret passages in the second floor of Lyran' fortress?

You can not sell or buy at the begining of the game. You must get to Buldar's Gate to buy or sell. I can give you a teleportaition code if you want. Hold R1, L1, X, O, square, and triangle and press start.