Hi,
I just bought two java ferns from ebay. It took four days for shipping. Advangage is, in that four days all the parasites would be died and the only thing that I have to deal is their next generation(if any). How about bacterial?
Disadvantage would be shipping charges which is high but not as high as buying a fish though.
what else?

Advantage in my case more selection my LPS carries very few plants. They look ok but nothing I really want in my tank. lol
Not to bad on the shipping cost if you get several plants at once. But I did have one shipment that the seller didnt put in cool pacs and the plants were soup when they got here. He said he would reship when it got cooler but never heard from him again. So just have to be carefull buying on line just like with anything else. I have a few sellers I tend to buy from as much as I can cuase I had good service with them before. Also go to some of the plant forums sometimes people well sell trimmings for the cost of shipping.
Good luck