Across chargers, vacuums, inflators, dash cams and audio equipment, the misleading numbers follow a small number of patterns. This is the method we use before writing about anything.
Red flag one: a peak figure with no continuous figure
Where it appears: speaker and amplifier wattage, jump starter amps, inverter output, vacuum suction.
Peak values are instantaneous, measured under conditions that never occur in use. The continuous or RMS figure is what the device sustains.
The test: if a listing gives a peak number and no continuous number, assume the continuous figure is unremarkable. Manufacturers publish the numbers that flatter them.
Red flag two: a measurement with no stated conditions
Where it appears: vacuum pascals, compressor flow rates, battery capacity, dash cam “night vision”.
A number without test conditions is not a measurement. Compressor flow at zero pressure is roughly double flow at working pressure. Vacuum suction with no filter fitted is not suction in use.
The test: look for the conditions. “20,000 Pa” tells you nothing; “20,000 Pa sealed suction, filter fitted” tells you something.
Red flag three: units chosen to look large
Where it appears: power bank capacity in mAh without a voltage, jump starter peak amps, storage in bits rather than bytes.
Capacity in milliamp-hours is meaningless without the voltage it is measured at. A 20,000 mAh cell at 3.7 V holds 74 Wh; the same product quoted at its 5 V output would show a much smaller number, which is why nobody does that.
The test: convert to watt-hours where you can. If the listing makes that impossible, that is itself the answer.
Red flag four: a standard named without certification
Where it appears: “HEPA-type”, “military grade”, “IP-rated”, “aviation aluminium”.
“HEPA” is a defined performance class. “HEPA-type” is a description of appearance. “IP-rated” without the two digits is not a rating.
The test: the real thing always has a number or a class attached, and the manufacturer states it.
Red flag five: a total split across ports or channels
Where it appears: multi-port chargers, USB hubs, multi-channel amplifiers.
“65W dual port” often means 65W from one port alone and considerably less per port when both are used. The per-port split under simultaneous load is the figure that matters.
The test: find the distribution table. Good manufacturers publish it.
Red flag six: reviews that are all from the first month
Where it appears: everywhere, and it matters most for anything with a filter, a battery or an adhesive mount.
Filters clog, lithium cells degrade, suction cups let go in summer. The failure modes in this category are almost all time-based, so week-one reviews describe a product nobody owns any more.
The test: sort reviews by most recent, and read the ones from six months in.
Red flag seven: compatibility stated as a category
Where it appears: CarPlay adapters, OBD scanners, TPMS kits, speaker fitment.
“Works with all cars” is never true in these categories. Adapters depend on head unit firmware, scanners on manufacturer protocols, speakers on physical depth.
The test: find your exact make, model and year on a supported list before buying, and check the returns policy, because compatibility failures show up immediately.
A short pre-purchase routine
- Identify the one number that determines performance for this category.
- Check whether the listing publishes it with conditions.
- Check the per-unit split if the product does more than one thing at once.
- Check recent reviews, not early ones.
- Confirm compatibility against your specific vehicle.
- Check what the consumables cost and whether they are sold separately.
Six checks, a few minutes, and they eliminate most bad purchases across every category on this site.
