For kaiser, make sure the tilt aspect of the device holds. My first one got really weak that when you'd tilt the screen up it'd fall right back down.
For both, kaiser and raphael, slide it open and close a couple times and watch out if its smooth or not. Theres a ribbon cable that connects the top half of the device to the bottom half, if you hold the device up to a light while sliding it you and sometimes make it out (look between the screen and kb). Look at the edes of this and see if they're freyed at all. If so stay away.
Also the obvious, check for physical damage, take off the battery cover and battery and look at the heads of the screws and see if they've been messed with. They should be black and will show silver if they've been scratched (i.e. opened up with a screw driver).
Look for the warranty sticker, if its not there, stay away. On the kaiser if you take off the battery cover it'd be the hole thats on the top right. There should be a sticher in there that says void in white.
press every button and make sure it works. Open up new note to test the keyboard.
when you take out the battery, look for a white kind of fluffy sticker. If its blue that means the phones been subject to moisture/water.
I'd say thats about it, don't worry if the device runs slow or any of the software part of the device because that can all be flashed and customized.
last note, i'd go with the raphael over the kaiser.
good luck and enjoy your new device.
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