Any musician that has ever attempted to buy or research any musical instrument has probably encountered the retail site Musicians Friend. They have a very large selection of musical instruments and assorted accessories. They have detailed descriptions and customer reviews that help in the purchasing decision. I've purchased many things from their website and more often than not I've been very pleased. I endorse shopping at your LOCAL music store as much as possible. I've learned many invaluable lessons from the good people at my local stores, and I am lucky enough to have more than one to choose from. I understand that some people are not in that particular position. Simply, they do not live within 100 miles of a store that sells a selection of instrument and the internet is the best solution for them. In most cases, a purchase is aided in immeasurably ways by putting your hands of the item you want to buy.
Having said that, a savvy consumer can use EBay to save a great deal of money on your next musical purchase. I am not endorsed by EBay, Musician"s Friend, or any other retailer, I feel that my experiences may help my fellow musicians. You may be skeptical of used instrument, and I am too. I also recommend that you check out the return details and read description thoroughly. There is always a reason someone want to get rid of whatever they are selling. Be sure the reason isn't that the item is broken or problematic. I can't speak in depth on making large purchases, like high end guitars or complete drum sets ( there doesn't seem to be that much of a value in drum sets when shipping is considered). Things that really seem to be bargains are effects pedals. You can find them for about 50-60% of retail. Cymbals are another great chance to save some money. Again, prices here hang around half price and shipping doesn't break the bank.
Don't forget you get what you pay for. If something seems to good to be true. There is a learning curve to using EBay, but the time it take to learn the ins and out is worth it.
