Reciprocity
People feel obliged to return a favour; give something genuinely useful first and the yes comes easier.
Reciprocity is the rule that people feel obliged to give back when they have received. Robert Cialdini names it the first principle of influence in Influence: The Psychology of Persuasion (1984). Give something real first and the other person is more likely to say yes when you later ask.
To use it, lead with a genuine, relevant gift before any pitch: a specific teardown of their process, a useful introduction, a sample that solves a small problem for them now. The favour has to feel personal and unconditional, or it reads as a transaction and the effect disappears.
It works when the gift comes first and unprompted, and when it is clearly for their benefit rather than a hook. The mistake is an obvious “gift” that exists only to trigger the obligation, like a mass-mailed trinket; buyers see through it and it can even cost you goodwill.