It is extremely common for people selling animals to sell in pairs. If that is the way they sell, that's it. You can always ask, some will, some won't. If you don't want the pair move on to the next seller. I sell pet supplies at flea markets, and know what it is like to deal with buyers. I have a set price and will not come down on it in most cases. I had to buy the items, get them to the market and pack back up. I have rent to pay and a profit to make. I know that there is a difference selling live animals over goods. No one is forcing you to buy that(or those) birds.