It's less about your skills, and more about your presentation. "Honestly" and "Trust me" smack of salesmanship. It's a weird effect. Engineers try to be more persuasive by picking up, intentionally or not, vocabulary used for persuasion. Unfortunately, there is a lot of nuance that's hard to control.

Tighten up your writing, and perhaps speech, so you simply state the facts as you see them. This router will meet your needs because it has these 3 features. 1,2,3. It's much harder to argue with flat statements of fact as opposed to the salesmanship trick of, i would lie to most people but i like you so i'm going to tell you a secret.

Or, you know, don't. If it's not a problem for you don't waste time on it, but that's the underlying effect.

My point: you're a random stranger saying to another random stranger "trust me" without justifying your request to trust you. Why should I trust you?

Your reply: After I've convinced them that I know enough to fix the problem (by either demonstrating my expertise/qualifications/experience or getting someone else to vouch for me), they believe me.

Well duh! If you demonstrate why they should trust you, they'll trust you. They won't just randomly pay you money to fix shit if they don't trust you.

Trustworthy people don't need to tell others to trust them.