My 4 Rules For Posting Testimonials:
1) Post testimonials of people they know
When people see testimonials of people they know, they trust you more by association.
Post testimonials of their friends (even better, their competitors.)

2) Talk quantities, not feelings.
Which testimonial is more likely to make you buy?
A) "I'm feeling great about this program. I've been enrolled for a week and already making progress."
B) "I made $10,000 in my first week on this program. Aiming for 20 now."

3) Use them to solve objections
Ask them what made them almost NOT buy from you.
This allows you to solve objections, build trust and get social proof in one move.
It's also way more real. And in a world where most testimonials are fake. people appreciate that.

4) Start with the best then switch to the rest.
Prospects will (maybe) read the first 2 testimonials and then skim over the rest.
At that point it's not the quality of the testimonials that matters (they won't read it anyway), but about how many there are.