Ask everyone, not just the happy ones
It is tempting to only ask the customers who smiled at you. Do not. Google's policy says a business must not selectively ask for positive reviews.
The ACCC, which enforces Australian Consumer Law, says leaving out negative reviews can be as misleading as posting fake ones.
Asking everyone is also what makes your reviews believable. A page with a couple of ordinary reviews among the good ones reads as real.

