Must agree with iterate, you do appear to make stuff that game-devs would be the most interested in, but you need to provide these game-ready to make them more attractive to buyers. I'll do my best to explain "game-ready" as it isn't written in stone anywhere. Hi-poly is more about showing off what you can do rather than providing a model that someone can simply import into their game engine and be ready to place it in the world they've created without it having a detrimental effect.
Game-devs expect models to be exported using quads, efficiency is more important than how pretty it looks. Atlas mapped models are most attractive because they only require a single draw call, split models with multiple textures are complicated and take a lot more CPU time, and therefore a burden on the game.
If you're making props, for instance, you don't want or need a high-poly, CPU eating model of a crate in the background that no one will ever interact with. If it's a character model then you can usually afford to be a little more elaborate. Supplying PBR models is always a good thing, game-devs can omit whatever maps they feel are too heavy but they would struggle to add new maps that aren't provided.
When I do game contracts I generally provide the base, normal, roughness, metalness and height maps as standard, sometimes, but rarely, I will be asked for the AO map.
In short, just make sure that your model is low-poly, PBR and as optimised as possible. You should provide the model in a commonly used format such as FBX or OBJ, and the end-user should be able to just import it and be ready to use it. This is game-ready.
If you're using something like Substance Painter then you can bake a hi-poly normal onto a low-poly mesh which will save a lot of subdivision to get smooth edges or base detail. Something to look into anyway.
Good luck with your model's mate and may you sell a million.