This is absolutely true. I also ask my clients for customer contact information and reach out to them until I have enough subjects.

Do not be discouraged by the no’s. Starting with friends and network is an option.

It also helps if you have a code of conduct/governance documentation for them to read and understand how their data is gathered and used.

I usually send a copy of all data to my subjects with a thank you letter and how it helped (with a gift card).