Is increasing the price of a commodity when paying by check (20%) over its cash price (200 dinars in cash and 240 dinars by check) due to a shortage of banknotes considered usury or exploitation of circumstances?

It is permissible to sell goods on credit for more than their current price, as long as usury is not involved. The original principle for a bank check and a certified check is that they are immediately cashable and their receipt is considered actual possession. It is permissible to purchase gold, silver, and currencies with them. However, an uncertified personal check is not considered possession. Since a bank check, when deferred, is not considered possession of its amount, it is therefore not permissible to purchase gold, silver, and currencies with it. However, it is permissible to purchase other goods with it at a higher price. The merchant must be gentle with people and avoid exploiting their needs.