People trust other people, so your ability to get people to endorse your product will be a strong influence over your ability to sell.
Set up timed sequence to follow up with buyers of your products to ask them for their honest feedback.
Recognise that people are busy.
Respect their time by making a clear ask, and offering something in return.
If they got value from your product, they'll leave you a nice review:
Follow up and say thank you, build deeper relationships.
Then, identify people who left a particularly glowing review, ask them an additional favor, and offer something even more valuable for their time.