Hi Don,
Sorry it took me a while to respond. I believe that I can get the Big D Odor Removal from amazon, so I got that covered

When I go to the used car lots and do the free demo, would I use a whole can per car?
(1) Whole can!
Does the vehicle's A/C unit need to be on for better results?
(2) For the DEMO....I like to make the "Fogging Effect" as dramatic as it can be, so I don't want anything "filtering out the fog". For the "regular" service, Yes....the AC could get into more crevices.
Do I need to vacuum the car first or just use the Big D Odor can as the vehicle is?
(3) We charge an extra $20 for vacuuming....however, we will drop it to $10 per vehicle IF....he let's us do his vehicles TODAY! I call this a "closing tool". And....we like to do the vacuuming first.
Is this a one time service per vehicle?
(4) Yes! Unless someone has smoked when going for a "test drive"!
after the process is done, Do I need to recommend the owner to let it sit for a few hours?.
(5) No! When the fog clears it's ready to go!
Any tips on the selling strategy? for example how to negotiate or ask for more business? and also, any selling points to focus on?
(6) Some of my '"students" just want to do the Big D while others will bring
(a) Headlight Cleaner and clean ONE headlight (IF it needs cleaning)...then ask if he'd like you to do Headlights too for an extra $X. If not, clean the other Headlight and forget this guy for headlights.
(b) If the door handles, mirror backs or bumpers are not bright black....do 1 or part of 1....and ask if you can brighten these too.
Don, I apologize as I may sound a little paranoid but like I said earlier I am in a tight situation right now and I really need to make this work. Thank you again for being very generous with your help and time. God Bless.
Jovany