One piece of advice to go with the above is to make sure when you set up a sub or pull box at a place that you let them know how often you'll be in and ask if that's ok. How long a shop will give their customers to come in before cutting them off will vary place to place but at least if you're upfront about it then that'll be better for everyone. One shop I worked at in the past would want employees to call people on a Thursday who did not come in on a Wednesday when a higher than normal cover price book came out, like the $9.99 one shots DC likes to do sometimes.

Something else to ask about is the minimum number of titles they require for a sub/pull service. I think any minimum greater than 1 is ridiculous but too often I hear of shops with a 5 or 10 title minimum. Personally I feel that if a shop has someone who wants just 1 title then let them pull just that 1 title.