Last year, digital ad spending worldwide soared to a record high of $209 billion, edging out TV marketing ($178 billion) and claiming the title of highest-budgeted ad medium for the first time. With so much money on the line, online advertisers stand to lose big if they can’t find solutions to what is—for marketers—perhaps the internet’s hardest truth: A large portion of those interacting with ads haven’t the slightest desire to actually buy products; in fact, they don’t feel any human desire at all.

Traffic bots are simple computer programs that commit ad fraud en masse by mirroring consumer behavior. Their point is to inflate the earnings of an ad publisher by forcing marketers to pay for false clicks, impressions, or conversions. John Gillham, CEO of blockchain-based marketing platform Adbank, estimates that online bots are responsible for half of all online traffic. In addition, a study by White Ops claims that 20% of all ad-enabled sites are fraudulent. Botted results can be notoriously difficult to detect; however, there are steps agencies can take to safeguard their bottom line.

Evaluate Traffic Sources

It’s healthy to be suspicious of a traffic source that provides abundant clicks with little to no conversions. Vetting traffic sources to see if a client’s site is performing as well as its traffic indicates can spare agencies a soiled reputation. Advertisers should open a feedback loop with clients regarding traffic results, and review analytics to make educated choices concerning the caliber of site traffic. Another option is hiring an ad fraud detection service—such as DoubleVerify or Trust Metrics—to detect and filter malicious traffic before it does any damage.

Avoid Shady Publishers

Publishers that refuse to communicate over the phone shouldn’t be trusted. Publishers blacklisted for being untrustworthy may create alternate personas to keep the ad fraud cash flowing in. Even if their accent matches a contact’s nationality, intent is easier to gauge when speaking in real time than over email. Slip-ups and inconsistencies that can be masked in text are harder to hide when talking in real time. Trust your gut, and if a publisher can’t be reached via phone, it’s probably best to cut ties.

Know Where Ads Are Placed

Not all ads are an ideal fit for every site. Obtaining a catalog of possible sites allows you to evaluate where marketing will likely perform best. Look for sites that are relevant to what you’re selling, have high conversion, and don’t show any signs of ad fraud. Honest publishers usually have no problem providing a list of sites where your marketing will appear.