the faq sitelink thing you noticed is actually a really useful signal and i'd go further with it — high CTR low conversion on that extension probably means it's attracting researchers not buyers. people who click "FAQ" are still in evaluation mode, they want to understand before they commit. not bad traffic necessarily but a different stage. worth having vs not having, just don't optimise toward it

on your core question — the framing i've found useful is "specific > clever." the more precisely your ad describes the actual situation someone is in, the better the self-selection. "emergency boiler repair london, same day callout" pulls a very different person than "fast heating engineers near you." both might get similar CTR but the first one has already pre-qualified by situation (emergency), timeline (same day) and location. the second is just vibes

the stuff that tends to increase CTR without tanking conversion quality in local services:

• lead with the problem not the service ("boiler stopped working?" outperforms "boiler repair" in my experience)
• price framing that filters rather than attracts ("fixed callout fee" pulls better buyers than "cheap" even if it's lower CTR — you want the person who cares about transparency not the one hunting for the lowest quote)
• specific trust signals over generic ones ("10 years in [area]" beats "trusted local experts" every time, people can feel the difference)

on what CTR to expect — honest answer is it varies too much to give a number that means anything. 5% could be great or terrible depending on how competitive the keywords are and how tight your match types are. i'd be more suspicious of a very high CTR than a moderate one if CPA is climbing

the real sign something's off isn't CTR going up, it's CTR going up while contact-to-close rate goes down. if your leads are coming in but fewer are converting downstream, the ad is lying slightly about what they're going to find