I've found the challenge is in keeping the Bonsai healthy, rather than it's health when I buy it.

I always seem to struggle with under/over-watering and keeping the right temperature to make the tree happy. I've never been great at keeping plants alive/healthy, but I love being around them.

I have a Chinese Elm, which is in a moss ball base, rather than a traditional base - you submerge the base in water...and just typing this comment has reminded me that I need to feed it (d'oh)