Most complaints about a trap that “does not work” are siting complaints. Four decisions cover the majority of them.
Height. Host-seeking mosquitoes fly at the height of a host — roughly 1 to 1.5 metres for a standing person, lower for a seated one. A trap hung at 2.5 metres on a wall catches a fraction of what the same unit catches at shoulder height.
Shade. During the day, most species rest in shaded, humid vegetation. A trap in full sun is a trap in the wrong room. Put it at the edge of planting, under a canopy, or against a shaded wall.
Wind. A plume that is stripped away never reaches an insect. Shelter matters more than exposure: a corner, a hedge line, the lee side of a building. In exposed sites, lower the gas flow and move the trap closer to cover.
Distance to resting cover. Traps work best within a few metres of where insects rest, not in the middle of a lawn. If the catch is thin after a week, move the unit three metres before changing anything else.
None of this is a specification. It is the difference between a product and a result, and it is the part a distributor can teach a customer in five minutes.