How can I be sure my laptop actually got serviced?

I’m thinking about taking my eight-year-old laptop over to Best Buy for a deep cleaning and some thermal paste replacement $67(it’s actually never been opened before). The fan kind of stutters for a few seconds right after I power it up, and then things start getting weird. First off, does it even make sense to pay for service on an old machine like this, or should I just toss it in the recycling bin?

Also, how can I actually be sure they aren't messing with anything else inside while they have it for $67? I definitely won't be opening it back up myself to double-check—I watched a few tutorials on YouTube and honestly, it looks way too complicated for me. I suppose I might already know the answer to that... I'd probably have to just take their word for it, right? I tend to be pretty skeptical about these repair shops, and since I'm spending $67 on a device that probably isn't even worth $233 on the used market (I'm not really sure what old laptops go for these days), I just want to feel confident that the job was actually done right.

The temperature readings before and after will tell you everything you need to know.
It’s not rocket science once you’ve actually done this a few times. Older laptops are way easier to crack open and clean compared to those ultra-thin modern ones.

I’d actually recommend this shop. I’ve brought two different laptops there, and both times the temps were significantly better after they were done.

It’ll run you $50—they swap out the thermal paste and do a full cleaning.

http://www.servislaptopa.com/

If you're really nervous about tackling this yourself, it’s probably better to just take it to a repair shop. Just be careful—you don't want them to try and upsell you on things you don't actually need, like claiming they have to wipe your hard drive or reinstall macOS from scratch. I mean, let's face it, everyone's looking to make a quick buck these days, right?