It's not my type of game, so I'm looking at it as an outsider to the genre. Take these opinions with a grain of salt.
I appreciate that it appears nicely polished. I like the UI theme and the audio events on button hover, etc.
The long list of items was a bit much as a novice. A tiered progression system, with item unlocks or tutorial level with 5-10 items might have been nice. Customers often came in asking for things I didn't have, so I wasn't sure if I was supposed to close shop and go buy it, or just dismiss them.
At first, I didn't realize I was supposed to reduce prices offered to the vendor from 100%. I guess I expected they'd give me wholesale prices by default. And I didn't have any sense of how low could I offer, nor how high could I sell. I guess that's the whole point of this type of game? Would a probability indicator be out of place? I like that it's a press your luck mechanic, offering too little or requesting too much, but I didn't feel like I had a sense of how hard I was pressing my luck.
Overall, good entry. I just need more exposure to this type of game.