I've received a lot of knives "LNIB" that were in worse condition than ones I received described "used". A knife can, literally, be Like New In Box, but have mechanical or cosmetic problems from the factory.
In fact, a knife can, literally, be mint in box, but likewise have problems in manufacture that don't have to do with how 'new' or 'mint' the knife is.
It's really easy to avoid this sort of stuff by giving a detailed overview of a knife's condition. Not to toot my own horn but here's a template I use all the time to describe the knives I list for sale.
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Model
When was it produced if there is no date immediately apparent?
Is this a limited run, and if so what is its serial number?
Be specific about 'Limited edition', this can mean any of several things and without specific information it is hard to accurately determine the facts about the knife.
Blade
If the knife was used, please say what it was used for.
What is the blade steel?
Have there been known issues with this particular steel in this particular knife or series of knives? If so, have you ascertained, one way or another, that this issue is not present in the knife you are selling?
Are the grinds and bevels completely even? If not, provide a photo showing the extent of the unevenness.
Is the edge intact? Either way, provide a photo.
Has it been sharpened before? If so, with a wheel, with stones or with a Sharpmaker/Wicked Edge/Apex Pro, etc.
Is there wear on the blade and where is it? Provide a photo.
Is the tip intact? Either way, provide a photo.
Are there any visible signs of corrosion or discoloration on the blade or the edge? Provide a photo if there is any.
Lock
For front-opening knives:
Describe how much blade play there is between the chassis and the blade.
Mention any slowness of firing from any angle.
Describe if there is any stickiness to the button or actuation switch.
Mention if there is any play or inconsistency in the button or actuation switch when firing. This varies from model to model and some is normal.
For D/A automatics:
Please disclose how strong the blade fires and whether it locks 100% of the time.
Mention any lockup difference between manual deployment and automatic deployment.
Disclose if the knife's automatic function has been fired while the knife is already in the open position after being manually deployed. This can severely weaken the leaf springs in some models.
Framelocks/linerlocks:
Describe how sticky the lock is. Some buyers don't mind stickiness but some do.
Accurately describe the strength of the detent.
Mention if the lock can be pushed further across the blade tang.
Describe the amount of play and whether there is any lock rock.
Provide photos of the lockup with the angle dead on so that an accurate picture of how far the lock has traveled can be obtained.
If there is a significant difference in lockup with a quick deployment versus a slower one, provide pictures showing this difference.
Arc locks/Axis locks/etc:
Disclose the strength of the spring keeping the lock in the open position.
Pushbutton automatic knives:
Disclose whether the blade has play in the closed position. This is a problem for some button-locked knives but not for others.
Describe the strength of the spring that resists when the button is pressed.
Describe the strength of the coil spring firing the blade.
Disclose any wear on the stop pin as this is evidence of excess wear that may result in blade play after more actuations.
Scales/Chassis/Frame
Document all wear, scratches, etc. no matter how slight. Provide photos.
Are all the screws seated properly and flush?
Are any of the screw heads stripped?
Are there any inconsistencies from the factory in terms of fitment? Provide photos.
Is the backspacer contacting the blade?
Is the blade stop properly contacting its respective pin/cutout?
Misc.
Is the pocket clip tension good?
Are the screws on the pocket clip loose or stripped?
Disclose missing or aftermarket parts and provide photos.
Does the blade actuate positively?
Describe the speed and smoothness of the deployment.
Does the knife come with original packaging and paperwork?
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It seems like a lot, but it's just a ten minute job, max, and removes almost all uncertainty in your listing so that people interested in your knife will know what they are getting. This takes away the confusion from nebulous terms like "LNIB" and "used" that don't actually say anything about the knife.
Here's a sample description made from this template:
Model:
Terzuola ATCF, made 1988. Three-screw clip, no blade steel marking. Full Ti scales with G10 backspacer.
Blade:
ATS-34, satin finish drop point, completely even bevels and grinds. Never sharpened and never used. Intact edge and tip as shown in photo. No wear on the blade, corrosion or discoloration.
Lock:
No lock stick, perfectly solid with no further movement across the blade tang. No play or lock rock. Detent is strong on both opening and closing and no significant difference in lockup with a flick or a slow opening.
Scales:
No wear or scratches except for one small mark as shown in photo. All screws are perfectly flush with the scales and none of the screw heads are stripped. No backspacer or blade stop issues.
Misc:
Pocket clip tension excellent as are pocket clip screws. Smooth and quick deployment. No box or paperwork.