They look pretty decent, could be improved a lot to reduce repetitiveness and the material setups looks a bit sub-par.
One thing to keep in mind however, is that the kind of people who purchase art assets are probably not the people that are very experienced with materials either.
Plugging them into the respective slots could be easily done, but I think a lot of your potential customers will have trouble setting them up to be used with a landscape material.
And unless you use any of the various techniques available for getting more textures into each 2d sheet, you’ll get stuck at the 2D sheet limitation of SM5.
I think if you improved some of them a bit so that they’re not so repetitive (example; the last one get a grid pattern due to too drastic variations in hue at the edges) and built a proper landscape shader with layers for each texture, the price would be fine for selling in marketplace.