Let me try to answer your question one by one...
1. Is it ethical to buy and sell pets?
Yes, it is ethical. Its normal human psycology that we realize the value of something only when money comes into the picture, in that same way we understand the value of pet when we pay for it (less value less money, more value more money). If you say that this is unethical that to buy and sell pets, then how do you want pets go their respecive homes?.
2. Equating pets with other livestock trade will actually improve life of pets?
No and obsolutely no, livestock such as hen,cattle, sheep and pig are targeted for specific end products and where as pets like dog, cat and birds are only targeted to give peace and happiness for the pet owner. In other livestock trade, you might be knowing that chickens, pigs, cattle are grown in small cage and they are also carried out from one place to another place for trade in small containers/dirty environments. If we follow the same process for our pets, I dont think so that this will improve life of our pets.
3. Why pet trade should be treated differently compared to cattle?
Because from Bill Gates to Billing Agent, everybody wants pets but only farmers need cattle. So the treatment is different.
4. Is it possible for the pets to get better life,without the trade in pink of its health,notwithstanding the legislations ,laws or selfserving NGO's?
Yes, its possible if we too start following the animal rules and regulations from european and american countries.