Silence is counted against you
Marketplaces measure whether you respond, not whether you take the work. A request you ignore lands in the same bucket as one you fumbled, and on most platforms that number affects how often you are shown to the next customer.
You have usually already paid for the lead by the time you decide it is not yours. Declining costs nothing extra and keeps the thing the payment was meant to buy — your standing in the listing.
Decline in one line, and say why
Two sentences are enough: what you do not do, and one concrete reason. "We do not take structural work — we are a handyman crew, and that needs a licensed contractor" is a complete answer that costs you nothing and reads as competence rather than rejection.
The reason matters more than the politeness. A bare "sorry, not us" leaves the customer with nothing; the reason leaves them with a better idea of who to look for, and that is what they remember.
The ones worth reconsidering
Out of area is a softer line than out of trade. A job forty minutes away is a bad deal on its own and a good one if it fills a day, or if the customer manages three other properties. Ask what the job is before deciding it is too far.
The same goes for jobs that look too small. A small job for a property manager is an audition. A small job for someone who just bought the house is the first of several.