Ratchet's reaction is fair and justified. Most people would be uncomfortable with the idea of someone else rooting around in their body—especially one that is unqualified or untrustworthy. Hence why he suggested he prove himself.

"After a period of study, I would take the same examinations you took to certify yourself. Obviously, we lack the documents detailing typical exam contents, so you would have to devise the test yourself, nor do we have the resources for hands-on training, so I would suggest replacing that with simple observation of my performance in the medbay. Even though most of my work will be with organics, it should give you an indication as to how I would treat you in a similar situation," Ratio says in a long-winded explanation. Essentially, by working with Ratchet for a prolonged period of time, he hopes it will instill the autobot with confidence.

"Would that suffice?"