People dealing in hessonite garnet can identify this stone just under the basis of its appearance (heat-wave effect) and color (orange-red, brownish red, orange-yellow). But 100% confirmatory test can only be made with the help of gemological instruments (refractometer and spectroscope).
Hessonite garnet can be identified with heat-wave effect which appears as hazy appearance or distorted appearance inside the stone. For a common buyer it is not possible to identify hessonite garnet just by visual appearance because they won’t be able to make out how heat-wave effect looks.
There are other gemstones (yellow sapphire, yellow topaz, natural yellow zircon) in trade which appears similar to hessonite garnet so it is difficult for a common buyer to identify if a gemstone is hessonite garnet.