We do not charge differently for bookkeeping for various marketplaces. This is because we have defined processes for handling the data from all of the major ecommerce platforms and payment gateways, that allow us to be similarly efficient regardless of marketplaces. This lets us simplify our charging structure by reference only the total number of orders and the number of payment gateways and marketplaces we have to reconcile (rather than splitting it out per marketplace/gateway).
Currently we handle bookkeeping for all Amazon marketplaces, both FBA and FBM, Shopify and several of its payment gateways, Wix, Magento, Etsy, eBay, Shopwired and a few niche ones. If you are on a marketplace we have not encountered before, we will typically charge a slight premium for the first bookkeeping period which will depend on how complex parsing the data from this payment gateway or marketplace is.