How would people even make a market bot? Like vitaminoos and shevarollers? do these guys make there own? how would one even learn these skills, would these individuals ever give away their bot?

It could be done easily in something like Python supplemented with databases with a bit of know-how about each. Python is easy to learn and has lots of libraries and stuff to build on. Databases are fairly simple too. It's just a matter of committing to learn something like anything else you do.

Start from the bottom. Make the bot log in and make functions to do everything you want such as search for an item, update a price, buy something etc...
Then fill the database with cases and or use maths to calculate price cut offs and stuff.

Then just set it up in a big loop to run constantly checking prices, updating items and all that.

Would they ever give it away: Not likely. Think about it.