An undercover Marketplace investigation exposed evidence some dealerships sell unnecessary service and push regular maintenance much sooner than the manufacturer recommends.

Following the report, Marketplace host David Common and expert mechanic Mark Whinton participated in a Facebook Live, answering questions from viewers about their vehicles and how to determine what needs doing when at the dealership.

Be very suspect if you hear a dealership service centre saying you need to get your throttle body cleaned, a fuel injection flush or a brake fluid flush, Whinton said.

Here are five questions and answers covered during the Facebook Live on Saturday:

1. How important are the maintenance schedules in a car's manual?

Whinton: It's critical and it's the bible. You do what it says in your service manual by the person who built your car. You do not go by what your dealer tells you.

2. Is there something owners should say yes to on an annual basis?

Whinton: Yes there is. You should have your car inspected. Remember it's looking, not saying you should have something replaced every year, except for in the case of engine oil. No matter what your mileage is, you should be getting your oil changed once a year.

3. If a mechanic tells you something is bad, like your brakes need to be replaced, is it your right to refuse service?

Whinton: Absolutely in any jurisdiction in North America you have the right to refuse the service that's recommended to you. This isn't surgery on your child. This is a consumer item. It's an asset…thank you for your advice. I'm going to get a second opinion.

4. When do you keep putting money into an older vehicle and when do you throw in the towel and replace it? 200,000 kilometres?

Whinton: Keep driving that car until you think the value of it is less than $2,500. That's what I would say. Because that's the cost of buying a used car that would pass a safety and an [emissions] test ... I've seen cars go up to 500,000 kilometres and more, so you can be a lucky one.

5. If you get your own mechanic, does that keep the warranty intact?

Whinton: Don't believe the nonsense from the dealer, if you take it somewhere else it won't be covered. You need to take it to the dealer for warranty work. An independent garage can't do that.