Definition
Alternative form of spoil the market.
How People Actually Use It
When someones availability as a partner is significantly compromised due to the apparent involvement with a somebody else. Market spoiling is not exclusive to those in relationships.
"Guy 1: Ayy you posting your girl on the gram? Guy 2: Naaah, don't want her to spoil my market. Spoil my market = (ruin the probability of other females sliding in his DMs)"
Source: Urban Dictionary