Fear not. NASA is going about this the right way, they know what they are doing. Really. Some wag once noted that the original Viking Mars landers would not have been able to find life if they had landed in the JPL parking lot.

We don't know what extraterrestrial life is like, especially if it is microscopic. We don't know what the exact chemical clues will be, for either a positive or negative result, so all we can do is look for the most basic environmental and bio signals we can. To this day, some of those Viking results are still ambiguous and contradictory.

As the local conditions are thoroughly assessed, and false alarms are eliminated, we will be able to refine our instruments and ask better questions.

There is no way to unambiguously identify or rule out life remotely, even the familiar life we find here on earth. The starship Enterprise scanners could detect "life forms" from orbit, we can't (unless a camera picks up a cactus growing nearby or an insect scurrying across a lens). So we search for water, or proteins, or some biochemistry we suspect might be common to exobiota. We look for unusual things and then argue if they might be due to alien biology. But since we don't know what alien life might be like, we can't really design an instrument to detect it.

And of course, there is the question of economics. Payload space is so expensive we must design sensors and probes to have the most
likely chance of finding anything of value rather than the ability to positively identify (or rule out) a thing we can't even specify. Like I said, we don't really know what we're looking for yet.

And finally, there are the resource allocation aspects of this search to be considered. With a finite. variable (and indeterminate) amount of funding available, program managers would rather spread it on many cheap missions to many worlds for recon than on one highly expensive capable mission to one world that will settle the question once and for all (but for that world only).