Like kopehagen, I always keep it short and to the point. I don't explain or justify my reasons, just a simple 'unfortunately, I am not able to provide pick up on my items' etc is all I say.

Occasionally, I will arrange to meet someone elsewhere, but it's only places I normally travel to in my daily errands. (Had someone ask me to go way out of my way to their work place so they could save on less than $2 postage... Just no. ;\ )