Why do you sell them for birds? It's up to the customers' discretion to use them or not.
For future use,
in case of harm from a bird toy (or anything else): There is something called an implied
warranty of fitness for a particular
purpose. If a manufacturer
knows an item is going to be used for a particular purpose, the item has to be reasonably fit for that purpose and the mfr can be sued for damages if it is not. Just like a baby teething ring for human babies cannot be made of toxic materials, a toy which anyone would expect that someone with a beak would chew on, also cannot contain materials so toxic as to kill the critter. This is true even if the manufacturer was unaware of the toxic nature of the paint or other defect, and in some cases a seller who buys from the manufacturer and then sells to a party who is then injured can also be held accountable despite lack of knowledge.
Of course, it is better to simply avoid items that one thinks might be a danger, but if for some reason you, reasonably not aware of the danger, use a product made for a bird and it kills the bird because of a manufacturing defect or problem, the manufacturer cannot simply tell you it was your choice to use it and disclaim responsibility for the death that way.