Riba On Non-Consumable Item Or Rent
This is a pure economic transaction and based on the available information, it could be due to poor decision making on the part of the tenant or undue exploitation done by the seller. However, even in this scenario, the difference between riba and rent can be understood. Had the needy person taken a loan on interest and he would have spent that amount in purchasing the filter. Now he is required to generate the principal amount of money plus the interest which would burden the person twice, hence riba ( being demand of profit on loan ). In case of a machine taken on rent, if on any occasion, the tenant fails to pay the rent, the machine still belongs to the owner and he can take it back anytime without putting any additional burden on the tenant as it was the case with loan. However, if the seller is charging unsual rent to exploit the situation of the needy person, then this is definitely unethical and the seller will be sinful. However, this does not fall in the specific domain of riba but in the general domain of consuming wealth of others through unfair means ( Quran 4:29 ). Riba is one specific application of the general principle described in Quran 4:29.