Some primary indicators...(not 100% guaranteed):
Sales receipt (with the name of the seller) and original warranty cards.
All original manuals in new condition (operator, handbook, schematics).
All complete original "goodies" bag (rubbers, plastics, fuses, etc), including promotional items included with the game when released.
Used games almost NEVER have all these items, including lightly routed games.
Serial numbers will match, and will look brand new.
They will be BRIGHT green, there will be little if no dust.
You will see no trace "heat bubbling" on PCBs due to lack of hours operated.
Ribbon cables will be bright white coupled with the same boards above.
No heat means no dirt which collects to electronics, unless the game was kept in the Middle East in a sandstorm.
They will not smell like smoke, look like tar, unless the owner was a chain smoker in their basement.
Connectors will not be burnt, traces undamaged, unless neglect by the owner.
Pure black, white, or natural wood, no dirt or carbon from coils.
The only way this can be generally faked is if a game was rebuilt from scratch or cabinet was swapped.
However, not guaranteed, as I will give an example.
I purchased an Embryon that had MPU "crib death", but was routed for 3 months and REBOXED!
Cabinet was white but still had around $50 in quarters inside.
This was not "HUO" seller..."Here's you sign".
Game play meters (non-CPU memory controlled)!
They are RARELY faked, or "rolled back" like a car odometer.
Operators in older titles install them, and sometimes in new games with electronics as well "old school" style.
This was not often a factory standards after 1975?, operator's "choice".
Home user don't normally put 90k plays on a game either.
Sellers forget about this one with "HUO" claims...oops...
Shooter lane can be faked, playfield swap, or "regrind" with sandpaper.
Playfield can be faked with re clearcoating the playfield, new plastic sets, "Treasure Cove" treatment, etc.
Cabinet can be faked with re decaling, and new labelling including serial numbers.
Coins mechs and coin doors are replaced all the time.
Coin door lock bars and bolt holes are STANDARD for certain later games of age, so that is NOT an pure indication of a routed game, BUT were generally considered an "option" at the factory later on for cost. Operators sometimes bought games in bulk, and then opted to sell them for profit beyond a route, all with lock bars still in box. If there is wear on the holes and lock bar, I would be suspicious.
If an owner wants to go through the trouble of properly faking a "collector quality" HUO game (purchased NIB), it is a TON of work, but is still possible if they REALLY know the manufacturer methods of the title and age.
Attached is a photo of a HUO backbox boards of one of my games.
It is 22 years old purchased NIB in 1994.
You can spot the "real deal" directly.
The reality is you pay for "condition" not "HUO" although some people are really picky about boards and playfields matching in serial numbers.
HUO games can look like complete $#@! due to neglect.