The first section here will go over guitar amps by category, and give a general description of how likely it is to find them used or not. The next category in this section will go over the actual buying process, and what the person who intends to purchase one needs to look for to ensure that the used guitar amp they are choosing is up to an acceptable standard.
Used Guitar Amps by Type
Used Acoustic Guitar Amps
Right off the bat, used acoustic guitar amps will be pretty difficult to find. If you do manage to find one for cheap, do not expect the prices to be as low as some other models. While it is possible that you can find one of these used, it should be thoroughly inspected to ensure that it is authentic for its purposes. If possible, ask for a demonstration using an acoustic guitar, and get more details about it. You do not want an imitation for this type of amplifier.
Used Bass Guitar Amps
These are more likely to find used and reasonable if you are searching around for solid-state types. The other type will be covered after this bit about used bass guitar amps has completed. The thing you want to look out for here is that it has the right equipment with it, or, more specifically, that you have the right equipment if it is not included. The proper loudspeakers are one of the key components of a bass amp, as well as other bass-related tweaks.
Used Tube Guitar Amps
All that can be said here is good luck. You will likely need it. The only feasible way that a person can get their hands on a used tube guitar amp is if it has been damaged in some way and requires repairs. These are some of the rarest available due to obsolescence in the production market, and are treated more like a collectors item in many cases. Only serious musicians need apply when it comes to purchasing these models of used guitar amps.
Guidelines for Purchasing Used Guitar Amps
Inspect the visuals. You will want to scrutinize the thing for any signs of damages. If there are broken connectors, bolts absent or loosened, or malfunctioning transformers – take your business elsewhere. This is perhaps the most novice way to tell if an amplifier is in good condition: seeing if everything checks out on the appearance front.
Strum the sound. This is one of the best ways to see if any used guitar amps are up to snuff when it comes to what you want from them. Plug in your chosen guitar and strum away, playing a song with chord progressions that you are familiar with. While playing, take notice of the sounds that the amplifier is emitting. If you like what you hear, you can move on to the final test, which is a general look at the capabilities of the chosen amplifier.
Stress the limits. Make sure everything is unplugged at this point! With the amplifier turned on, crank up the volume as high as it will go. From here, you can scrutinize what you hear from the speakers that come from the amp when it is performing at maximum. Remember that some noise is fine, but really obstructive or bizarre noises are a red flag to move on, since these can indicate that the amp has been worn out.
You can follow these guidelines and get yourself a nice device for playing back whichever guitar style, model, type or categorization you choose from. Most importantly of all though, just follow your gut instinct. If you like what you get from it after following these guidelines, then go for it, given that what you purchase is worth what you pay for it.