@heroeric, if I recall correctly, he literally complains to the woman that her price is not market value indicating he thought, at the very least, he would get equal the market value for the materials. This is in a world where the internet is available to MC. Take, for instance, in our world, the AK-47 and arms trafficking. I just did a quick search and found market value prices for the AK-47, at least in the U.S. from one site range from $550 - $1300 depending on brand, model, and other accessories. International prices seem similar with highs reaching close to $8,000 for special and/or banned rifles sold in areas they aren't usually available. Doing a quick and vanilla
(not venturing to Dark Web) black market comparison, I found that depending on global location an AK-47 can sell for as low as $75 and as high as $15,500 with the average worldwide price of the AK-47 settling around $540. Of course, this isn't getting into all of the nuances about models, specialties, etc. The point I'm making is that market value and illegal market value change depending on a variety of things, most specifically the availablity of resources. That's how economics works.
So, for MC to go into a black market without actually doing his research = silly.
For MC to go into a black market without knowing the price he wanted to sell his materials at in order to bargain (that's why he got taken advantage of) = silly.
For MC to go into a black market thinking he'd automatically get market value = silly.