If you want something from someone, you should think about giving them something first. This has to be done with the genuine desire to help of course; and not a half-arsed attempt to create guilt by manipulation.
I walked out of Phuket airport recently and stopped to get my bearings. A nice woman came up to me as asked if I needed help. She came across as genuinely wanting to help and not trying to sell me something.
I asked her where the ATMs were, and she kindly pointed me in the right direction. Before I could walk away, she politely asked if I would like to help her with a little survey. After she had so kindly given me clear directions, I was happy to spend a minute with her on her survey – and this was after getting off a long-delayed and super-packed flight and being held up in immigration for ages.
Had she just came up and asked if I wanted to do a survey, I would have said no outright.
Same thing with business practice. It has always worked well for me to meet each client with a genuine interest in helping them and adding value to their business. I don’t hold back ideas or thoughts. And this is before I have even been engaged to do any work. Most of the time, this approach ends up in the client engaging my services. And all of the time, they walk away feeling like I have given them something of value.