Ah, I dont sell the source code with most of my Pico-8 projects for a few reasons.
One is that if people are purchasing it to get a better understanding of how to make a game then there are other projects of far better quality to pay for, the underlying code is not suitable in most cases to learn from.
Two, 99% of the source code for most of my games is available for free on lexaloffle.com (I should probably do a round of updates to make that clearer and/or provide direct links).
Three, I make games that should be completely playable and complete without ever paying money. That payment is just for more content if someone liked it and wants more, and the bit I protect (the bit that has actual value). The underlaying game structure doesnt change between the free and premium versions.
Four, there are enough people/bots out there which try to steal content for their own websites to make money of my work I avoid giving out the extra bit of work. This might change in time if I decide to alter the methods I make money off the games, so maybe at some time in the future it may or may not become available.
I think I will try to get around to more directly pointing people towards the freely available source code.