So I was on my way to Gun Runners one day and ran into a random merchant. I knew he wouldn't have much weapons, but I offered to buy. When the merchant showed me his inventory, he had an Anti-Material Rifle for 5,000 caps. I didn't want to spend my caps all on one thing. So I ran off. I finally approached Gun Runners and I saw they had a Anti-Material Rifle for 2,000 caps higher, 7,000. I didn't have that much so I returned to the spot where I had met the merchant and waited. The merchant was there after I waited 3 hours. Now here's where it gets weird.

I opened the merchant's inventory and noticed he now had a brand new set of items, some old. I saw a Brush Gun I had seen earlier there but for a cheaper price then before. I also realized that the Anti-Material Rifle wasn't there. I thought that was strange so I went back to Gun Runners to get an Anti-Material Rifle. I knew I didn't have the caps, but since the Brush Gun in the merchant's shop was cheaper, I had hope. I peeked inside the inventory at Gun Runners and saw that they no longer had a Thermic Lance or a 10mm pistol laser sight like my previous visit. The Anti-Material Rifle was still there, but for 9,000. Not only was that ridicolously high, but the prices had changed again! So I went on a journey to trace every price of every weapon in the two merchant's inventory.

Day one:

*Gun Runners:

*Anti-Material Rifle: 8,000 (lower than the day before's)

*Varmint Rifle: 5,000 (has changed once since my first visit, by 2,000)

*9mm pistol: 4,000 (3,000 lower than first visit)

*12.7mm pistol: 6,000 (was not there in first visit)

*Missle Launcher: 8,000 (had not changed since first visit)

*10mm pistol: 3,000 (4,000 lower than first visit)

*Cowboy Repeater: 6,000 (not there first visit)

*Brush Gun: 7,000 (had not changed)

*Random Merchant:

*10mm pistol: 5,000 (was not there first visit)

*9mm pistol: 4,000 (1,000 higher than first visit.)

*Brush Gun: 6,000 (had not changed.)

Day Two:

*Gun Runners:

*Brush Gun: 5,000

*Cowboy Repeater: 7,000

*9mm pistol: 4,000

*Laser Rifle: 5,000

*Plasma Pistol: 5,000

*Assault Carbine: 7,000

*Hunting Revolver: 6,000

*Hunting Rifle: 8,000

*Random Merchant:

*9mm pistol: 6,000

*.357 magmum revolver: 6,000

*Silenced .22 pistol.

*Service Rifle: 7,000

Day Three:

*Gun Runners

*Trail Carbine: 6,000

*Varmint Rifle: 7,000

*Laser pistol: 5,000

*Marksman Carbine: 8,000

*Sniper Rifle: 7,000

*10mm SMG: 5,000

*Anti-Material Rifle: 8,000

*Random Merchant:

*12.7mm SMG: 6,000

*Brush Gun: 7,000

*9mm SMG: 5,000

*Caravan Shotgun: 6,000

*Riot Shotgun: 7,000

I tallied up the results, but it just doesn't make sense. Is it the AI system that lets AIs but stuff, or is this just normal? I had never seen this before, so I'm concerned.

Wait, wait, wait, a 9mm pistol was 4000 caps and the Varmint Rifle 5000? My 9mm pistol price is 124 caps.
Why would you want the AMR when the Brush Gun is less expensive and is better?

Actually: http://fallout.wikia.com/wiki/Brush_gun and http://fallout.wikia.com/wiki/Anti-materiel_rifle

Brush Gun's ammo is less expensive, its 1-2 hit kill to most things, even deathclaws. AM Rifle is 1-2 hit kill to most things, even deathclaws.
AMR is bolt action- slower
BG is lever action- faster
BG's dps is higher, way higher.

and would it hurt you to actually post the DPS and DAM of the guns or whatever you wanted to show me?

Only things I can think of:

Merchant inventory doesn't always stay the same...eg, they have a rifle for sale, but next time their inventory turns over, it won't be there...or at least, the exact same one may not be there...and something else will be. I've noticed that a lot....if you see a weapon mod you want, if you decide you'll come back for it later, but in the meantime inventory has changed, it may not be there anymore. Very random. I think that's normal.

If their inventory changed, is it possible that the weapons you saw before were in less repaired condition? I believe the condition of the weapon affects the merchant price. If they were all fully repaired condition, however, I dunno.

Edit: Also, can't remember if you're on console or PC...obviously a mod could be changing things, but only if you're using them.

I have to research that, but I think you're right. I think it's normal.

Yes, but it's weird the weapons weren't there every day.

Not on a PC. Though you can have mods for consoles.

Yeah...if there's a glitch going on, it sounds like it'd be inventory changing every day instead of every 3 days. I've seen doctors inventory change every single day, but usually not merchants...maybe a wandering merchant, but the GunRunners? Not in my game at least.

That is it exactly. Gun Runners sells guns that are 100% repaired, so they will be the most expensive. Other vendors will sell less than pristine weapons. Not sure if all the Gun Runner Merchants sell pristine or not.

Pretty sure the merchant at 188 Trading Post does.