I don't really know but if the plants are not housed in anything but water and other plants I don't see why they would. I personally don't buy plants off ebay. I do use aquariumplants.com in the US if you reside in the US. Every plant I have purchased has been in great condition and larger than expected. If you're looking at online ordering anyway, you might want to find a reputable online dealer like the one mentioned above or somewhere in the UK if you reside there.
Some people I do believe will give their plants a potassium permanganate rinse before putting them into their tanks. I just give it a tap water rinse.