I would say yes and no
. When I first started buying orchids I bought from Ebay and it was a matter of impulse buying and what I liked I bought. Probably 40-50% of my collection is from Ebay.
I no longer buy orchids from Ebay as my great friend up North says they are not worth it- that they are mostly dogs
I don't think you will generally get any orchids that are showbench worthy or will win awards but you can ones that are still pretty nice and will give you personal pleasure which IMO is as important as whether or not someone else will tell you if it is a worthy plant or not.
IME quality depends on the seller, I have been extremely happy with many, satisfied with most and only dissapointed a few times. Same with commercial orchid nurseries I have bought from.
You should always check the catalogues and prices of nurseries and compare with the prices -division/plant size of orchids you find on ebay.. you may find for example a plant that is selling on ebay for some price such as $30 or more can be bought as a $10-$15 seedling from a nursery
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Another thing to beware of is getting sucked into to the whole bidding and winning against someone else thing- it can be as bad as gambling
Set a limit and stick to it!
Unless you know the quality of a seller's plants, it is preferable to see the *actual* on auction that you are bidding on and if won will receive. If they don't have a photo of the plant, ask them for one.. if they can't be bothered taking and sending a photo then forget about it!
Check the wording and info on postage cost and responsibility. Sometimes there will be a picture of a bloom and a plant in a pot but you're not bidding on that actual plant in that picture! Also some sellers will not take responsibility if the plants go missing or get damaged in the mail- find out how much it costs [from the delivery company/service] and offer to pay the extra for insurance/registration.. in Australia it only costs $2.60 for up to $100 of goods.
Hope that helps