I have checked the website and found you're in Beijing.Sincerely hope you have a good time there:-D
Han‘s explaination for 回头客 is really perfect
回头you can understand by “look back”
客 means 客人 customer
Customers who really like to look back several times .Why?Because this restaurant is highly recommended as his view.He likes to visit and have meals more often.
And if you click 回头客 on that website，it will turn on the commendation from the customer who come here more often.The owners hope customer to see that because 回头客 represent this restaurant is really great.
Hope that's helpful.:-D