Liking
People say yes more readily to those they like; genuine similarity, praise and cooperation build it.
We'll figure out the right fit together
Liking is the simple principle that people prefer to say yes to those they like. Robert Cialdini lists it among the six principles in Influence: The Psychology of Persuasion (1984), noting that similarity, sincere compliments, familiarity and working toward a shared goal all increase liking.
To use it, find real common ground, offer honest and specific praise where it is warranted, and frame the work as the two of you against the problem rather than you against them. “We’ll figure out the right fit together” positions you as an ally. Small, genuine touches matter more than charm.
It works because trust is the gate every argument passes through, and liking opens it. The mistake is flattery that is obviously instrumental, or forced similarity; both register as insincere and make the buyer trust you less, not more.