Hi and

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As far as picking one out at the LFS, look for one that is active and overall healthy looking. Fins in good shape, not bloated, ect. But, breeders I don't know, I've never dealt with one. Others here have though, so they can tell you.
Other than that... Try not to use plastic plants as they can snag delicate fins. Silk is better, but make sure there are no sharp pionts on the stems.
They like warmer waters, so a heater is good.
Be careful not over feed, especially dry foods. Some bettas tend to be prone to constipation, which can lead to a whole lot of others problems. Frozen blood worms are usually a favorite, my boys love them!
My brain doesn't seem to want to work right now, so other members will be along to fill in the parts I missed

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Good luck to you and your future beaty!
Erin