As long as you get some sort of warranty (30-90 day at least), you should be fine. If something is gonna f^ck up (thats caused by defect, not user error), it will usually happen right away.
yes, i bought one 12' l7 and it was refurbished and it works fine. the onyl thing that made me mad was that the chrom magnet was all scratched up. it is like they set the sub on cement. but i am running mine at 1 ohm with rms power going to it and it works great.