When a customer brings their printer in to you, they are likely to be frustrated because their printer isn't working.  What they will be looking for is to be reassured and to know that their printer repair will be as efficient and convenient as possible. And if you can deliver this, they will be satisfied customers.

The first time that you meet your customer, you should be looking to engender confidence.  The way to do this is to be both polite and friendly, and be knowledgeable without being overbearing.  When you are discussing the problem with your customer, make sure that you are listening to their version of what is happening.  The key is to try and pick out the bits of what they tell you that will be relevant, and use that to help diagnose the problem that has led to them looking for printer repair.

Once you agree that they will leave the printer with you for the printer repair, be realistic about giving them timescales about the repair.  For example, telling them that you will call them at the end of the day when you know that you have an afternoon job will only frustrate them, whilst telling them you can have a look at it in the morning and will call them about midday will set their expectations at a realistic level, and you will sound more knowledgeable when you have been able to have a full look at the printer and what will be involved in the printer repair.

Whatever you have told the customer, and at whichever step of the printer repair you are at, make sure that you are delivering on the promises that you make, and that you keep giving the customer the realistic timescales.

The other important aspect of the printer repair is to ensure that once you have looked over the printer, you always give your customer your quote on the work before you get started, as they may not want to go ahead with it.  Whether or not they give you the go-ahead for the work, take either decision with good grace. And even if they don't give you this work, by remaining polite and professional, they may well consider you for the next job.