Identity checks: what actually stops fake listings
A directory dies of fake listings before it dies of anything else. Recycled photos, agencies posting under twenty names, phone numbers that ring nowhere. Visitors work it out in about two visits and stop coming back, and the honest advertisers leave with them because their listings are sitting next to the fakes.
The three checks, in order of what they cost
The cheapest is the phone. A code by message, once, before the listing goes live. It costs a few cents and it removes the bulk of the noise, because whoever posts the same advert on forty sites is not going to hold forty numbers. It proves nothing about who the person is, and that is fine: it is a filter, not an identity.
The second is the photo. Not a check on the person, a check on the image: has this file already appeared on this site, or on the open web. Duplicate detection catches the agency that recycles the same set across accounts, which is the single most common form of fake listing and the one visitors notice first.
The third is identity, and it is the one that costs. A document plus a live selfie, matched by a provider. A few cents per check, and it settles the questions that phone and photo cannot: is this person an adult, is this person real, is this the same person as last month. It is also what a payment processor and, increasingly, a regulator will ask you to show.
What to do with the result
The mistake is to make the check invisible. If verification only lives in your database, you paid for it and nobody sees it. Put a badge on the listing, let visitors filter for it, and say plainly what it means. Verified advertisers then get more contacts than unverified ones, and the incentive does the rest of the work for you.
Do not make it mandatory on day one either. A new directory with three advertisers and a hard requirement stays a directory with three advertisers. Make it optional, make it visible, make it pay off, and let the market close the gap.