I had a friend who was in the pawn shop business for a while. I asked him if individuals buying or selling instruments from/to a pawn shop was a smart move. His sage advice...
Selling:
If you have a guitar worth $1000 minimum on the used market, Guitar Center will offer you $600 maximum and won't haggle much on price. That same guitar taken to a pawn shop will have a $100 opening offer from the shop, they will haggle but at best will only go up to about 50% of what Guitar Center would give you.
They're logic is, if you really wanted the $1000 you'd sell it yourself; if you didn't want to hassle with advertising and tire kickers and shipping then you'd just take it to Guitar Center; and if you're bringing it to them they assume you're either too stupid to know what it's worth, or too concerned about what Guitar Center might see wrong with it, or you're in need of quick no questions asked cash. Net, don't sell a bass to a pawn shop unless you fit the fool, or the worried, or need fast money without questions category.
They assume once you walk in the door with that guitar it's staying there, or you wouldn't have walked in with it in the first place. Hence the 10% starting offer with heming and hawing as needed to fill space on the wall. If they have room for ten guitars and they already have 15 in stock, they're gonna stick pretty close to their opening bid, if they only have two on the wall you might get them up to $300.
Buying:
Pawn shops can be an occasional source of hidden treasures, but the vast majority of of the time that's not the case, most pawn shops are fairly good at determining the street value of a guitar. Where you find the gems is when there is a specific model year that might be a sleeper or a country of origin that might make a difference or possibly some after market modifications that aren't obvious but add value. Net, know exactly what you're looking for and how to spot value added features that aren't obvious (i.e. an Epiphone VP with lull pickups).
They assume anyone walking in their door is willing to haggle on price. So that same guitar that they paid between $100 and $300 for that has a minimum value on the used market of $1000 is going to be priced at its maximum used street value of let's say $1500 regardless of its condition. That gives them tons of haggle room and also room for discount tags to be hung on it occasionally. Yes, they will come down in price or even mark it down if they want to move it but not a whole lot unless they need the space for something else. They typically target a rock bottom sale price at 75% of the minimum street value, in this case $750 rock bottom.
As far as inventory is concerned it's a double edged sword. Pre Internet, they wanted things in the shop that created a draw since they really didn't advertise much beyond their store front. Now with eBay, Craigslist, reverb and other on line outlets they expect to have a much more rapid turn over but still need to keep some stuff in stock in the store for walk in customers, which is still a good portion of their business. The shops that are doing well have a normal size store front but somewhat less floor space than years ago, and now have a lot more storage in the back room or warehouse for the overflow and on line sales. Back to guitar specifics - I was told it's not uncommon at all to have a guitar in the inventory for years if the store relies largely on walk in sales, but with the internet they like to move things much faster than that, maybe six to twelve months max.
That's all the inside info I have and it's from about 10 years ago, but I suspect things haven't changed much.