Though I understand your view, I would strongly advise against displaying free hours on your invoice. It could just as easily be viewed as a passive-aggressive move, which is the exact opposite of what you want.

Even if it comes across the way you intend - what if there is a next time where you do not include any free work? You might very well be setting an unwanted precedent leading to unnecessarily awkward future conversations.

Just keep your invoice simple and bill the customer for the work - especially when they are satisfied. It does not seems you need small 'tricks' like this to build this customer relationship.

In short: The potential downside seems a lot larger than the upside, which is one of my simple ways of deciding on which actions to take.

Though I understand your view, I would strongly advise against displaying free hours on your invoice. It could just as easily be viewed as a passive-aggressive move, which is the exact opposite of what you want.

Even if it comes across the way you intend - what if there is a next time where you do not include any free work? You might very well be setting an unwanted precedent leading to unnecessarily awkward future conversations.

Just keep your invoice simple and bill the customer for the work - especially when they are satisfied. It does not seem you need small 'tricks' like this to build this customer relationship.

In short: The potential downside seems a lot larger than the upside, which is one of my simple ways of deciding on which actions to take.