When I used to sell a particular suite of computer software we used to use a pyramid.
We knew that if we phoned 85 companies we'd get to speak to the decision maker ten times.
For every ten people we spoke to we'd get an appointment to demonstrate it.
For every three people we demonstrated to, we'd get a sale.
Once you've worked that lot out, you'd know that 255 phone calls led to a sale. As above, knowing that made it easier to deal with people saying "no" as you knew someone would say "yes" soon enough.
You simply cannot expect every visit to result in a sale. Once you realise that, you can deal with it.
And for you, Tosh, with your buddhism, if they say "no" just experience it without judgment and move on to the next opportunity...
Vin