To be honest, I'm not my advice is going to be more convincing then what you already do. You seem to be doing an excellent job of being humble as opposed to proselytizing at least to me (such as in your caveat above that Julia also deserves credit.)
It is possible (I don't know how likely this is in your case) that attempting to focus too hard on sales techniques can actually backfire if the people who you are attempting to convince are too aware of sales techniques. For instance, after a long spree of consecutive contractor visits, I started to notice certain thematic elements. At one point, I'm pretty sure I had someone leave just because he used a certain sales tactic (I think it was 10% off, but only today!) simply because what might have been convincing under ordinary circumstances seemed like a transparent attempt at manipulation after being exposed to it repeatedly and I didn't even care whether or not his product was worth it.
I would say the only advice I can give you is to not give up. As you mentioned to TheOtherDave, getting an idea of what works is going to require talking to a lot of people. Getting shot down will be discouraging, (In fact, it will probably feel MORE discouraging than you expect, even if you take this into account) but you will want to convince yourself realize that it's better to just move on then spend time moping about it. Also, as someone who has spent time moping, I've found that moping doesn't necessarily feel like moping when you are moping. It would be a good idea to have someone else who could keep an eye on your emotional state during these attempts to note if you seemed to be moping to a more outside perspective.
I think that those pieces of advice (Don't give up, trust in your friends!) Are sort of generic advice that fits a large number of occasions though. Sorry I can't give you more helpful advice, but my record doesn't seem to contain evidence that I am usually that convincing.
When I started my new job at a startup about a year ago, I started getting about a third [1] of my pay in stock options. Being risk neutral in donating, I decided to spend my salary on me and donate any proceeds from my stock options. This let me increase the fraction of my pay I was giving away without decreasing what I keep. Mathematically and economically, considering just what I can give, I think this was the right decision.
The problem is, much of my potential impact is from convincing others to give, and if I have to talk about stock options, expected value, and money that I intend to give away it's confusing and distracting. Things were much simpler when we could just say "we lived on about $22,000 and gave about $45,000". Should I switch back to giving money?
It would not be an easy switch. Options represent a small chance of a lot of money, and they're not very valuable to me personally. (Each additional dollar is worth less than the last). If I were to start giving a third of my compensation away as cash, that would be about 2/3 of my paycheque [2]. Which would be pretty hard. Maybe I should donate some combination of cash and options? Making this more complicated, I had negotiated more options in exchange for a $10K lower salary, figuring that for money I was giving away this was the right thing to do. Suggestions?
[1] You might say "how can you say 'about a third' when you have no idea whether your stock options will even be worth something ever?" What I did was estimate how likely I thought Cogo Labs was to be worth $X in about ten brackets ($0, $10M, $50M, ...), and then calculate an expected value as $0*P_1 + $10M*P_2 + $50M*P_3... Then I multiplied by the fraction of the company whose options would vest to me each quarter, and got something about half my quarterly salary. So: one third of compensation.
[2] It's 1/2 my salary (the last third is options) but 2/3 of takehome pay because 1/6 of my pay goes to taxes and other paycheque deductions.
(I also put this up as a blog post)