It is never simple to deal with a client who is unwilling to pay for services well done.
Unfortunately, the world is full of individuals who tend to take advantage of Heating, Ventilation & A/C professionals plus other professionals.
In all my life as an Heating, Ventilation & A/C serviceman, I did not have to encounter such a person until recently. Surprisingly he was a commercial client whose chain of restaurants my friend and I had repair for a whole week. The units in the restaurants had been neglected plus required a lot of cleaning plus repairs to restore the a/c to its original status. Sadly, even after helping him get back the unit plus spare him the expense of buying new Heating, Ventilation & A/C systems for the weird premises, he wanted to be stubborn about paying us. His excuse was that my friend and I had not signed any agreement on the amounts, so he would pay what he deemed fit, however being a mature plus experienced Heating, Ventilation & A/C contractor with over three decades of experience, I did not have the energy to argue with him. Instead, I asked him to channel the payment through the company plus get feedback directly from the owners. That was a route he was unwilling to follow since he knew it might attract legal penalties. Finally, after a few minutes of push plus shove, he agreed to pay the amount owed. He even apologized for his stubbornness after his workers reported improved airflow plus comfort levels as reported by their purchasers. It turns out fake Heating, Ventilation & A/C servicemen had duped him that he only wanted to pay for confirmation.