We did not ask our customers to write us the testimonial.
BTW, the below feedbacks should be sufficient to explain:

After a sample translation:
"Congratulations that our editor thinks your translation quality is good."

One of our clients in the United State:
"You are fantastic."

One of our clients in HK:
"you are very easy to work with  - i am glad we have met." and
"you are the best." and
"I hope that you get more business from our NY office - I forwarded them your contact details and said that you were great to work with"

One of our clients in Singapore:
"Thank you so much. You are QUICK."

Also from the United State:
"I sincerely and truly appreciate all your attention to this job. I will recommend to my colleagues to call you more often with new jobs!"

One of our clients in China:
"You are so great and so kind! We will contact you first if any new Thai job."

Also from China:
"You are really so cooperative! Would like to work with you in the future!"

From the United State again:
"You are easy to work with and I appreciate your help."

And one of our Thai clients said:
"I like your translation style. You are part of our success."

Yeah, those are the reasons!