Google just published a new video teaching businesses how to hire an SEO. If you provide SEO services to clients it's worth taking a look at in case you run into a potential client that's come across this video:
I always charge upfront for a technical audit and then if they go with me, I deduct it from the monthly (over a 3 month period). No way am I giving a potential client anything that comprehensive on a silver platter. I learned that lesson a long time ago.