I am relatively new to this server (started last week or so). It might be me, but I can't buy things. To place a block, I right click. Usually, I buy things with right click also. When I right click the things I want to buy, it says No Selling Here (Left Click to Buy!). So I left click and nothing happens. I check my inv. and nothing is there. I still have my Rupees, but nothing in my inventory. I even tried switching my controls. My friend, Soccer_Taylor304, also said she has been having a problem. I'm sorry if it's just me or this question was previously posted before, but I need to know what is going on. Thank you.
Does it give you a message when you click it? Does the shop let you purchase items? Is it your own shop? Are you crouch-clicking? Does your MOUSE1 work? (Left click) Is your refrigerator running? Then you better go catch it!
I have actually had this occur for me aswell, when this happens to me, I take the equipped item and put it on my inventory. Try using an open hand and left click. For the shop signs, I think the left to buy and right to sell buttons aren't changeable.
Are you sure that the sign is correctly formatted? If that isn't the case, I would try switching your controls back to the default setting to buy/sell, and see if that works.