Ebay has become the best place to buy and sell analogue synths. The best place to buy, because you can take your pick from a wide selection of products, and the best place to sell because of the top prices these instruments command on there. Beware of junk being sold off. I have known people shift on worthless, damaged synths, with talk of cheap and easy repairs, for top money. Nothing is quick, easy or cheap when it comes to synth repair. Parts are difficult to source and repairers can ask what they like as so few people have the necessary skills and access to the mostly rare and expensive parts needed. Don't be affraid to ask lots of questions about functions. 'I haven't got the equipment to test it', or, 'I don't know how these things work', are danger signs. Avoid these sellers. They should borrow some equipment to test it, or take the time to learn about what they are selling!
Synths made by U.S or U.K. companies tend to command the highest prices. Edp Wasps, even in poor condition, regularly go for over £600, not only on ebay but also on other specialist and auction sites on the web. Minimoogs can go for well over 2 grand. Modern equivalents do not have the pose or long-term investment value. Japanese synths tend to be more reliable and better value. Yes, we all know that the Roland TB-303 makes silly money. It's all about supply and demand. Everyone wants the sound and the collector's value. Ignore people who give subjective views on synth prices. 'Never pay over...' might mean that you will never own! No one knows how much people want or are willing to pay for the gear. The market will dictate the price. Take care when buying analogue synths. Read up all you can and try to locate a nearby repairer. Synths to avoid include the Yamaha DX synths. They generally sound rubbish and are impossible to sell! I know this from personal experience. Ebay is the only place you have any hope! Let's all enjoy our music and hope for world peace!