The cons to buying a fish off Aquabid would be..
if the seller is overseas you'll have the added expense of import fees and shipping to the US. These fees generally are only about $10-20 more depending on what your transshipper charges you.
you also have to accept the fact that your fish could arrive dead because of mishandling during transport. Long finned fish are also prone to fin damage during shipping.
Its a little more expensive and there is a little risk involved but IMO if you get the fish you want it makes it all worth it.
*Be smart.. Do your research!!*