You're smart for recognizing the importance of building relationships...very few wholesalers in my area understand this. I don't buy from assignors for two main reasons...liability and fictitious numbers.
Most assignors in my area of Texas have virtually no concept of the real costs associated with an investment, including acquisition, hold, remodel and sale costs. That's because they've never purchased, renovated, or sold a property. I get calls weekly from assignors across the country who are surprised that I don't have any interest in their retail deals.
To gain investor confidence, ensure the investment property numbers are real, use the most common contract forms in your state (versus a 2 or 3-page) internet/guru contract form) with appropriate addenda, or an attorney-drafted form and attorney-drafted assignment agreement. Also provide tons of good / detailed photos along with property details critical for the investor to make a decision.