You've seen it in your personal life:
When someone gives you a gift, does you a favour or is continually nice to you...
... You feel an urge to repay them in some way.
Your customers feel the same as YOU.
And here's why:
The urge is down to RECIPROCITY and we all fall it...
... "I'll get the next round of drinks"
... "It's our turn to invite you round"
... "We can't turn up empty-handed."
So start giving your customers surprise Thank You gifts and exceed their expectations of what your company is like.
Treat them as individuals (not as numbers) and you'll enjoy all the benefits reciprocity brings.