Dealing with luggage left behind by passengers in the airport

What is the ruling if the price was unfair, so he cancelled the deal, but there is a penalty for the one who cancels it?

Ruling on offering an item for sale on eBay that is already on Amazon, selling it to the customers via drop shipping

Is Dropshipping Halal?

Selling a product at different prices to different customers

What is the ruling on charging fees in return for delaying payment until the time of delivery when buying online?

Ruling on buying apartments and shops before they are built, and on getting a discount if you pay in full up front

Is buying expensive items regarded as extravagance or excess?

Ruling on extra credit offered by phone companies

Ruling on selling phone credit worth 10 pounds for 12 pounds