There are so many companies which provide us the convenience to have any product by way of crediting. The question is whether the crediting are allowed in islam stuff? If allowed What percentage of gains can they take?
The difference between the buy now price and the buy now, pay later price is the interest element. Credit sales typically work by giving you the product now and the finance company lending you the money to pay for it now. You then owe the finance company the capital element ($200 in your example) as well as the interest element ($300-$200=$100 as per your example)
Riba is obviously haraam.