I've had a wonderful and horrible experience with ordering online. WetSpott is a wonderful place to order from. All but one fish out of 20 arrived safe and healthy, they were also very easy and nice to work with. Answered any questions I needed in a quick and timely manner. I highly suggest them.
For bettas, betta_mafia and water_pets are good sellers on Ebay. Although, when I had a question mafia never replied whereas, if I am remembering correctly, waterpets actually sent a message saying if there was anything they could help with to let them know without me messaging.
I unfortunately can't remember the seller I purchased from and had an absolutely horrible experience from, but another seller I would not suggest purchasing from is betta.time on eBay. A friend purchased from them and I was there when the betta came in. The betta arrived with a slightly damaged gill plate and had odd holes in the internal bag. I don't believe there was any IAL extract or M.blue either, which isnt a major thing, but is a good idea to have to reduce stress.
Aquatic Arts is based out of Indianapolis, which isn't too far from Kentucky, depending on what city you're in. Since I live in the city I go pick up my fish, but they package them up really nice and usually send a few extra. When I ordered 3 corys and 5 marimo balls, I got 4 corys and 7 marimo balls
I've bought from different sellers on Aquabid and have yet to have a bad experience. You are able to check the reviews on each seller before purchasing from them and you can message them to ask questions.