How do you figure out what is an upsell and what is necessary?

look at your owner manual, it will tell you the interval

For one thing you could stick to the owners manual. But some manufacturers have been taking some essential maintenance items off to make their vehicle appear cheaper to operate. These items won't affect the vehicle during the warranty period, but if you plan to keep the vehicle for much longer, as in 10+ years, then you are taking risks.

Another thing is extensive research on the vehicle. There are probably a few forums out there for your vehicle that you can join and see what others say about certain maintenance items. The only way to protect yourself from being upsold is to equip yourself with enough knowledge to know what is needed and what isn't.

For fuel injector cleaning, you could buy yourself some fuel system/injector cleaner for $10-20 and follow the instructions (which is basically to pour it into your fuel tank). If your vehicle is using port injection instead of direct ingestion you likely won't ever need intake valve cleaning. Intake valve cleaning can also be DIY'ed for $10-20 but requires more work. You likely won't need either service if your vehicle is under 100k km.

garmium wrote: ↑ I took my car in to a random garage for an oil change and they recommended "fuel injector and intake valve cleaning" I had no idea why or how so I declined it.

Should I have cleaned it? Also, in the future how do you know if a dealer is upselling you or doing a necessary service?

There really is no way to know unless you know a thing or two about your engine, your car, etc. Most vehicle owners lack the interest and knowledge to truly know if their cars would benefit from pampering that goes beyond scheduled maintenance. Owner's manuals are usually silent about these things (as mine is) but that doesn't mean that these services would not improve the performance of the vehicle.

So you can take the "it's not in the owner's manual" route and decline everything that isn't specifically mentioned - and there's nothing wrong with that. It's simple and it's usually the most economical route. Alternatively, you can try to learn - a good start would be to ask the mechanic what condition the recommended procedure is addressing and what is entailed in the recommended service. In your example, if they were simply pouring a fuel/valve cleaner into the gas tank, you could decline and then later do that yourself. OTOH, if what they were suggesting was a proper intake valve and injector cleaning, that could be a more labour-intensive (and costly) process that you might need to be convinced has benefits. I do all my own work and, on my car, a proper cleaning takes some time and I prefer to pour a bottle of Chevron Techron into my gas tank once a year.

FWIW, I am at 240,000 kms and I am at the point of deciding to keep the vehicle or move to something new. Depending on what direction I go will guide my decision about certain maintenance items - including cleaning the valves (which on my car would involve removing the intake plenum and other bits and "walnut blasting" the valves). Heck, on my car, it's at least an hour of labour just to be able to inspect the valves let alone cleaning them.

garmium wrote: ↑ I took my car in to a random garage for an oil change and they recommended "fuel injector and intake valve cleaning" I had no idea why or how so I declined it.

Should I have cleaned it? Also, in the future how do you know if a dealer is upselling you or doing a necessary service?

The "random garage" is your problem
You need to get "your own mechanic" and still do your homework ...

garmium wrote: ↑ I took my car in to a random garage for an oil change and they recommended "fuel injector and intake valve cleaning" I had no idea why or how so I declined it.

Should I have cleaned it? Also, in the future how do you know if a dealer is upselling you or doing a necessary service?

assume it will all be an upsell. your manual has a maintenance schedule follow that.

If the car has codes or isn't driving as it normally does that becomes a different story. look up to see if there is an owners forum for your car to see common issues. I dont believe there is such a thing as a trusted mechanic they are a business so your best bet is to educate yourself.

CaptSmethwick wrote: ↑ There really is no way to know unless you know a thing or two about your engine, your car, etc. Most vehicle owners lack the interest and knowledge to truly know if their cars would benefit from pampering that goes beyond scheduled maintenance. Owner's manuals are usually silent about these things (as mine is) but that doesn't mean that these services would not improve the performance of the vehicle.

Exactly. Pretty much every owner's manual will say that aftermarket additives are not necessary, but for certain cars history has proven that's not the case. That certain cars have certain problems that would benefit from additional maintenance. For example, carbon buildup in direct-injected BMWs need walnut blasting (intake valve cleaning), and oil burning Hondas need oil additive to help free stuck oil control rings.