A cute little game. I can see myself playing this a lot if the game is a little bit more polished.
The gameplay is pretty straightforward and chill, though there's really no end goal to the game apart from getting a highscore. Rejecting or selling too low also have little to no downsides. Furthermore, buying too high is risky since you can lose all of your money real quick. I think it would be interesting to have a certain amount of customers per day and a certain quota to meet, so it would involve more strategy in handling the prices.
Another feedback that I can give is to make the text have an outline, especially for the customer's dialogue. Sometimes the customer brought an item that is dark in colour, and that made it quite difficult to see what that person is saying. Having a white outline to the text should help with that issue, or at least having a slightly transparent background under the text.
Last thing, I think you should write down how much the expert and the multiplier cost. It's a minor thing but it would be pretty helpful.
Overall, cute and simple game.