It is well-known that the production-inventory problem for deteriorating items in the supply chain is a challenge when deciding on how many products to manufacture to obtain a maximum total profit. This research work develops an economic production quantity model for a deteriorating item under partial trade credit policy considering inflation, the effect of reliability factor of a production system, and the demand depending on the price of a product whose selling price is optimized. The production-inventory model is formulated as a nonlinearly constrained optimization problem by analyzing different cases. Finally, through a numerical example, a sensitivity analysis is performed to study the effect of different parameters, changing one parameter at a time and keeping others fixed at their original values.