Maybe I can shed some light here. Usually, we can't tell when a skilled technician-type person disassembles and reassembles their knife. It's the unskilled ones, of course with a lot of good intentions,

that really just screw things up! Disassembly and reassembly of a knife often is not a manufacturer's concern; it is poor reassembly and damage of knife/parts that will get the user into warranty fulfillment concerns.
Part of this topic relates to a liability issue. If a knife that has
not been tampered with injures a user due to a manufacturer's related issue, the manufacturer could be liable. But, if the knife has been tampered with, incorrect adjustments or incorrect reassembly could cast the fault to the user, not the manufacturer. We want our knives to work properly, thus encorage the user
not to tamper with their SOG knives.
But, you wanted to know how we'd know that knife tampering has occurred? Here's some good indications:
- If it is reassembled incorrectly
- If the teflon washers are missing or incorrectly reinstalled
- If screws are stripped or show signs of use
- If interior parts are broken or altered
- If it is in pieces

- If there is documentation (with high quality photography) on Cliff Stamp's web site showing and descriptively explaining how he tampered with his knife

These are just the big ones off the top of my head. We most often get someone who couldn't get back together, usually with the story that
"it just fell apart while on my night stand and I wasn't even touching it!...REALLY"
If the knife's action works smoothly and if there are no signs from the list above, we mostly can't tell (and don't really care a bit),
but a knife like this isn't likely coming back in for service! 