What would you do when you recommend a treatment to your patient, but it doesn’t turn out to be good, and the patient complains? How would you respond without harming your relationship with the patient?
Are you asking as a hypothetical question or a real world question? In an ideal world, you make things right to try and please the patient.
The real world answer is different. By the time the patient complained, the relationship is harmed already. So, you have a few options here, either make it right or refund their money/dismiss the patient.
Most of these cases can be mitigated via case selection and pre-operative patient management. If patient satisfaction is reliant on unwavering, unrealistic expections, you should have not taken the case in the first place. Give it to someone who likes to deal with those types of cases. You will never make them happy nor is it worth your time/efforts because the problem is with the patient, not you. Also, if you don't think the case is within your paygrade or skill level, don't take the case. If you are able to set the patient's expectations, do not overpromise, but overdeliver. That way, results meet or exceed expectations. If prognosis for the patient's desired treatment is poor, you must let them know of potentially poor outcomes. If they still decide to proceed, then it's on them. I stopped doing herodontics for the most part unless the patient can accept that it's a temporary and will need to be extracted at some point.
You will never satisfy 100% of your patients, nor should you ever expect to. Learning how to manage the pre-op, operative, and post-op is key. For operative, just work fast and don't hurt the patient. Now, to answer what to do with post-operative management, you have to understand what they are complaining about. Some people have really poor pain tolerance/anxiety/extreme pain aversion, and that usually requires pharmacological intervention. Understand why it didn't turn out "good" - if it's esthetics, know what the patient doesn't like, if your crown/restoration failed/broke, know why it failed and broke and make it better (more occlusal reduction is usually #1, bond your restoration if you have poor retention, etc...)
Ultimately, a practice evolves in that patients who end up having a bad relationship with you due to treatment failure will seek treatment elsewhere and life moves on as long as you have NP's to replace patients who leave. The ones that stick with you are the ones that remain in your recall hygiene department.