In my opinion, dont buy used coilovers.. ive looked around and found that alot people are selling TEIN SS and Budy Club N+ coilovers which they have used around 5000km-1000km and sell them for $1100-$1450.. for these prices, if you wait patiently and do you homework.. you'll be able to get a brand new one for and extra $150-$250.

And for TEIN FLEX used for 5000km-10000km people are selling them for $1700-$1900. and an extra $150-$250 you get a new one.

Just remember, be patient and do your homework.
Check US websites for prices and use them as a guide to see how much you're looking to spend.