What can possibly go wrong?

I visited service center today to upgrade my laptop's RAM and SSD. However, their prices were significantly higher than what I found online. Before leaving, one of the technicians discreetly approached me and offered to provide the same upgrades at the online price if I met him outside of the office tomorrow.

I'm skeptical about this proposal, and I'd appreciate some advice. What precautions should I take, and how can I verify that he's installing genuine hardware?

Update : I called him to my house and he installed RAM, SSD, cleaned the fans, didn't take any extra charges, saved me a little from what they were charging in the office, good service id say.