How do I decide the price to sell my amps and guitars at, how to sell them for the maximum price, and where to sell it at?
Thanks in advance. Sorry in this in the wrong forum?
Look at the price you bought it for new, the condition its in, and what similar items sell in your local market (craigslist, ect)

If you're really unsure, try putting it up too high, the worst that will happen is nobody will make any offers and you'll know your asking too much.

Try craigslist, ebay, guitar center (sometimes they don't give you squat)
Don't sell to guitar center whatever you do.

Just look at kijiji and craigslist ads in your area for an idea.
Generally 3/4's of the original price will get offers.

Some items are different though like cabinets for example, they tend to go for half price.
100w Peavey Valveking Head
Mesa Rectifier 4x12 Standard Cab
Ibanez RG 321
Boss DD-7
iSP Decimator x2
BBE Boosta Grande
Modded Crybaby
MXR Blue Box
Numark Power Conditioner
Korg DTR-1000
On craigslist, put up two adds. One for the price you would like to sell it at, and one at $100 more. GENIUS!
"If you're looking for me,
you better check under the sea,
because that's where you'll find me..."