Dennis,
I was phoned the other week by a cafe owner asking how much I'd quoted for all their chairs to be cleaned... I had never actually given them a quote but I quickly jumped in and told her that I'd do a free sample clean and email her a quote for the whole job... It gave me a chance to see what method would be best and judge how long the job would take.... They were delighted with the work and apparently their customers were commenting on how clean this chair was, I got the job and they want me to do it every 9 month....
So I think the free sample clean with no obligation is the way ahead and even if you don't get every job, the jobs you do get are well worth it....