Is that obvious? If this were as overwhelming an incentive as you say, we wouldn't have accurate breathalyzers for alcohol. But we do, and it's simple to see why. 1) Cops aren't the only customers; medical establishments, individuals, and workplaces also have a legitimate interest in measuring impairment. 2) Tech like this doesn't remain novel forever, it can be checked for accuracy, and if you made a device that exaggerated impairment your reputation would tank, your company name would become a political hot potato, and your sales would never materialize. 3) There is definitely a point in disputing the idea that cops are indiscriminate gangsters roaming the streets trying to lock up any citizen they don't like the look of. Police have their personal and institutional biases, but by and large, most are interested in tools that allow them to safely and fairly administrate the rule of law. Police don't have much career or institutional incentive to arrest someone for a DUI at a traffic stop or not—they just stop bad drivers and check. It's prosecutors who are trying to rack up conviction numbers as a matter of career advancement and political viability. But even that gets checked: their work will be subject to an adversarial legal system, at which point any evidence that the device doesn't work would come out in court and tank their conviction rate.
So... where do you see perverse incentives here, again?