I have a game, and I want it to occasionally offer the player an upgrade which gives them a more powerful sword for one life. How would I how about doing this?
Developer Products can be used completely with the MarketplaceService.
To have the player buy the Developer Product, use the PromptProductPurchase method (not to be confused with PromptPurchase).
When the player buys the product, you can use the PromptProductPurchaseFinished event (again, not to be confused with PromptPurchaseFinished) to award the user.