In the late 80's I bought a Pre ban, naturally, HBAR. Paid about $300. About 1/2 of what they were going for. Some yo-yo had taken a ******* file to the trigger and disconnector. Got scared and traded it into the LGS that I repaired guns for. Some idiots amaze me, what did he think no one would notice? Why not pull the butchered parts and buy new ones?
I was there when a local bought the AR, and had it back in less than an hour. He was mad. He was an ex-Marine who did Nam. He knew the gun was not legal, demanded and got his money back. The owner told me to take the gun and handed me a few boxes of ammo to test it. Yep, pull the trigger once and it didn't stop till the mag was empty. There was a deep lake next to where I was shooting. Threw the offending parts in the lake. He ended up offering me the gun for what he had given a fella for trade in. I ordered new parts and all was OK. Sold it in the early 90's for around 1K.
The prices have gone up and down every 4 years or so, depending on who might be pres. Or lately honest citizens have decided help is not really a phone call away and they may have to defend themselves.
It is sort of like the stock market, buy one, the price will go higher or lower but will pass your original purchase price once in a while, unless you paid 2K for a less popular Brand or model. Then again it is like the stock market, if you bought too high you have to absorb the loss and move on.