Ebay and vintage electronics are one of those funny pairs... You gotta take the bad with the good.
For me, local purchases are reserved for opportunistic scores, things that need to be tried or sampled first, or immediate need products. I am a hardcore ebay shopper for the things that can wait. As the saying goes... Time = Money. The same can be said for patience = money in relation to ebay. Even with shipping factored It is typical to save money buying on ebay, especially for electronics and photography gear.
I've been pretty lucky with ebay and have gotten pretty much what I expected from about 95% of my purchases. I buy boomboxes, tape decks, photo gear, tapes, and a whole smattering of other used and new goods that I know I cannot find locally without having to pay that "gotta have it now" premium. Sometimes I buy items that I know do not work and have them restored by a pro with the intent of owning it to play with for a while, then flipping on ebay. The key is to research your seller's previous feedback history before bidding or buying it now, I thoroughly review things the seller has bought or sold. Sometimes you will even see what they paid for the item you're bidding on. And if you have a seller with a low feedback rating selling $1 trinket items but has a mint M90 for sale with blurry pics and a vague description, then stay away. Read the listing forwards and backwards, and ask very specific questions to further asses the items condition and try to get a guage of the sellers' quality in the process. If I have ANY doubts at all, I leave it alone. Invariably, another of that same model number will come along.
And probably the best key to healthy and successful auctions bidding is to use a sniping tool. I'm convinced that ebay is a form of emotional warfare. And a good sniper will save you lots of money and keep you from making crazy-arsed emotional bids in a flurry. It helps win items for less just as much as it also helps protect you from yourself. Pick a comfortable maximum price, leave it alone, and force yourself to remain unemotional.
And if you don't win it (or lose by $1) then somebody wanted it more than you did. Just wait for the next one.