Tell him to set up another account at SportingBetUSA/SportsBook and purchase San Antonio Series -260 for a 30 cent hedge, while explaining to him what a scalp is and how it's important to line shop and use multiple books. [img]i/expressions/face-icon-small-wink.gif[/img]
In all seriousness, if he wants to cash in, you should give him a price based on whatever your shoppe's current selling price is for San Antonio series - in other words, if your shoppe's current SA Series price is -290, then it's a wash (you pay him +290). If your SA Series selling price is -270, then you owe the guy 20 cents. If your selling price is -300, then the guy owes you 10 cents. This is the "mathematically correct" way to handle it.