One of the main things here should be a visit to the seller to examine the unit. You should also have some knowledge about what it is you are buying.
It is important that you can look at the unit in detail and see if the tubes are in good nick. Seeing the machine runnig is also mandatory.
I would be very warey of buying from an auction site. And if you decide to do so make sure you can write off the money if it is a dud.
I bought a used crt from a forum member, had a good look at it and only parted with a small sum which i could write off if a dud. There are experts here who can secure the machine you want for more or less the same money you are talking about. And these people will install and give great customer care and aftersales.
I would love to give you a name but this maybe against forum rules, but think of the second letter in the alphabet and then the number between 3 and 5.

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