Just be yourself
Being genuine can't be faked. Customers can tell when you are seriously interested in the product or service you are selling, and they know when you stand behind them.
Source: Sales author Brian Horn
Along the same lines, your customers know when you're being yourself — even if they don't REALIZE they know this. Your customers are more likely to respond favorably and will more likely come back to you again and again when they see you as a real person or even a friend — instead of just a salesperson.