Bay-area catalogues split on the marketplace question by weight before they split on anything else. Terminal tackle, filters, sacrificial anodes, pool chemistry, cleaners, gaskets and sun shirts are precisely what a fulfilment network was built to move: small, fast, repeatable, easy to review. Bimini tops, screen panels, patio sets, enclosure hardware and anything that leaves the building on a pallet are precisely what it punishes, through oversize tiers, storage months and a return rate that eats the category. So the first deliverable here is not a listing. It is a line drawn through your catalogue, SKU by SKU, with the fee arithmetic written next to each one.
The second split is compatibility. Amazon has a genuine fitment system for cars and none worth relying on for hulls, engines and model years, which means the marketplace can sell the generic version of your product and cannot sell the part that only fits a 2016 outboard. That is not a weakness to work around, it is the shape of the channel: the marketplace does discovery on the universal SKUs, and your Shopify store does the compatibility resolution, the saved boat profile and the reorder. Brands that try to force the technical half of the catalogue onto a marketplace collect wrong-fit returns and a suppressed listing for their trouble.
Then there is the part of the account nobody watches until it costs them. Buy-box loss on a core SKU, an ASIN suppressed for an image spec change, a variation family broken so reviews stop pooling on the parent, stranded inventory sitting in a fulfilment centre with fees running. We work the catalogue first, rebuild Sponsored Products and Brands by intent and margin band with targets derived from contribution per unit after referral and fulfilment costs, and keep a weekly rhythm on search terms, negatives and suppression alerts. Advertising a broken detail page just buys traffic for whoever else is in the carousel.