The ones I have found are not doing anything illegal, just sharp and cynical.
Many now work on-line, some with dubious payment systems via 3rd-party agents who add their own costs and profit to the client company's fees, and display advertisements that may or may not be real but generally tell you very little about the supposed advertiser.
Some of these outfits - such as one that EP to which used to sell screen space - look at the user's internet activity to offer a possible partner living in your locality. It was of course a ruse - the apparent advertisement was simply a link to the "scam" home-page.
These have largely replaced the types who would buy full one or two pages in newspapers to display contact advertisements, but to answer required a telephone call to a premium-rate number which played a long, turgid recording about nothing too useful before even starting to play the advertisement-messages. These in turn had driven the simple "lonely hearts" ad from the papers.
And there are or were dating and adult-contact magazines, but these have gained a reputation of being largely peopled by prostitutes and in some, would-be illegal immigrants and convicts. One long-established British contact magazine charged £20 minimum to place an ad, plus £1/word for those above 20 words - but charged only the men. It was free for the women advertisers!
And who are these shady outfits?
Oh, they trade as regular dating agencies - but it is a cynical, parasitical trade that profits from its users' failures to find happiness, and its commercial impossibility of any sort of guarantee.
The telephone dating-services in Britain typically cost £1.50/minute. So the introductory recording, nearly 15 minutes, long plus 10 advertisements about 1 minute each, cost over £30 even before you find one that may be worth responding to. Of course, even if the ad is genuine and leads to a date, the company knows it can give no guarantee even that.
So not "scammers" as wilful fraudsters - the agencies are not breaking any laws - but the effect is the same.