The warning came after one activist investor took to Twitter to flag a potentially misleading advert she had seen on Facebook.
The Twitter user said she had had concerns about the ad's offer of independent financial advice and reported it to Facebook as a scam.
The advert claims to help people find a local independent financial adviser for free who can then provide investment options on people’s pensions.
The anti-scam campaigner said: “I called them first. I asked whether they have independent financial advisers and they told me that they are not independent.
“I have been contacted by another company after leaving my details. I gave [the lead generation company] a London postcode and although the company that contacted me offers independent financial advice, it's based in Manchester. Not so local.
“Its Facebook ad is misleading. The advice is not always independent or local.”
Advisers said they would not normally have the need to buy client leads in the first place.
In a tweet, Darren Cooke, chartered financial planner at Red Circle Financial Planning, said: “I don't and never have bought in leads. New clients mostly come by referral and some by finding the website from google.”
Likewise, Neil Liversidge, managing director of West Riding Personal Financial Solutions, tweeted: “We don't buy in leads. Most new clients are referred by existing clients. A lot are [...] people from our own and surrounding villages who've known me all my life, and a lot who've known me for years through motorcycling.”
Insurance brokers have been flagging suspicious lead generation adverts in their sector for months.
They have seen targeted adverts for life insurance or critical illness cover but, on investigation, found that data was being shared with several providers and the cover promised in the adverts was not the actual cover being offered at the end of the process.
Kathryn Knowles, co-founder of Cura Financial Services, told FTAdviser whenever she sees something she is "not sure about", she sends it to her contacts at provider AIG to investigate.
She also recommends fellow advisers to report the posts on social media as inappropriate.
Ms Knowles said: "A big problem comes from the fact that a lot of lead generation comes from marketing companies, that do not seem to be held as accountable as say brokers or insurers are.
"From this you have brokers that are buying these leads, without fully checking the credibility and ethics of where they are buying them from.
"You then have the brokers that know exactly where these leads are coming from, that are not massively concerned because it is not their in-house financial promotions."