If they buy the birds they are worried that the sellers will be convinced the market is good and work even harder to trap the creatures. If they take no heed, they fear the peddlers will mistreat or inappropriately raise the animals.
買下來擔心鳥販認為有市場，更「賣力」地捉鳥；置之不理，又怕他們飼養不當虐待鳥。