Payment processor for two different types of transactions?

Need some advice for deciding on a payment processor. We’ll handle two types of payments; firstly, your typical C2C transaction and the second being a bit trickier. We allow sellers to create a sales listing and based on how much they are selling an item for, take a specific amount. For example, if a seller makes a listing for $100, we’d take $1, $200 listing, we’d take $ 2, etc etc. does anyone have any experience here?