Valid & Invalid transactions

Q: I am a LP gas distributor. We supply retail and wholesale customers. We collect empty cylinders from the customers which are then exchanged for full cylinders. Customers only pay for the gas inside the cylinder. Sometimes customers return cylinders that still have gas inside for exchange. We are able to ask the retail customers if they want to return cylinders that still have gas inside as this is a loss to them. Most of them are fine with the loss. However, it is impossible to check with the wholesale customers as the cylinders are returned first to the wholesaler who then returns them to us. As a result we receive an average of 250-350 kg free gas per month.

1. Can we re-sell this gas that comes back from the customers?

2. If it is not permitted, what should we do regarding our past sales from this 'free' gas?

3. The retail store is run entirely by non-Muslim staff. Is it permissible for the shop to remain open during Jumuah?

Q: Since there are lots of rules of a valid transaction (I have read in Behishti Zewar), if a person purchases something with an invalid transaction, will that thing be haraam for him to use or eat?

Q: I would like to know if I can deal in the following ways:

1. Sell a product on an online platform and receive payment (part or full) but the product is not in my possession.

2. Sell a product on an online platform and receive payment (part or full) but the product is in the stock of my supplier who promises to send me when I have confirmed the order.

3. Being the official rep of a particularly expensive but slowly moving product, can I take orders with part or full payment and then place the order with my supplier?

Q: While doing wholesale business with Amazon, one buys the product from a seller in another country and then drops it off at Amazon. We shall be advertising the product and Amazon will be responsible for storing, packaging and shipping of the product and it will charge us fee for these services. Is this method of sale correct.

Q: Forex trading currency through mobile app from standard bank. Money is transferred to shyft in rands, which can be used to purchase at any time through a physical card or virtual card. Rands can also be traded for four specific currencies. These currencies, if in possession can also be used for purchasing through a virtual card. From what I read, no interest is involved and no hidden costs. Only fees for trading between currencies and amount is agreed before confirming transaction. This is called shyft from standard bank.

Is it permissible to use?

Q: Is it permissible for a supplier to:

1. Sell/enter into deals for goods not yet in his possession (not physically present), but the goods have been paid for. The goods maybe in transit or for some other reason not yet in his possession.

2.) Sell/enter into deals for goods he has neither paid for nor does he have them in his possession.

3). Sell/enter into deals for goods that are in his possession but have not yet been paid for. (Purchased on credit)

Q: Is it permissible to buy an item from a kaafir who has not yet taken possession of the item? Further if a Muslim sells an item which he has not taken poseession of, will it be permissible?

Q:

1. Is it a valid transaction when a company pays money to buy electricity from different countries?

2. Is it a halal job - ensuring that people get proper line of electricity and maintenance of electrical plants so that electricity connection remains proper?

Q: I work at the airport at a car rental. Now if a customer comes and wants to pay in Euros but we accept only Dinars, to make his work easy I take the Euros from him at the current exchange rate at the airport knowing that the exchange rate will be better outside in the city. So I accept those Euros and use my Dinars to give to the company and later take those Euros and exchange it in the market at a better rate for myself or sometimes I wait for an even better rate. Is this money halaal? 

Q: Many people do business and import items from foreign countries. Due to our country charging tax on the items imported, many people get the item invoiced at a lower price in the foreign country so that less tax is paid. I would like to inquire regarding the permissibility and rulings regarding this.