One of the changes they made included putting the pet in the trade window the same color as the pet being transferred. So you know you are actually getting a blaze cu sidhe and not a plain one.
One old pet scam that was used on Test Sosaria by a 9 year old girl (hi! T! ) and her brother who was maybe 11 (hi! A!) was used for scam trading of rare pets, and boy did we have some very rare colored pets on that shard.
Using two accounts, make a character on each with the same name, name a regular pet the same name as the rare pet and stash inside a building nearby, then using circle trans transfer the regular pet with same name to the player buying in the actual trade window.
This was before they added the pet's color to trade window. I think they maybe also added the pet's breed to trade window? If not then this would still work with say a nightmare and a dread mare named the same thing and held by two accounts with a tamer of the same name on the two accounts. The nightmare is held inside a building next to the dread mare being sold so it is not seen unless using all names before trading. It would work for pets that look similar in the trade window if the breed is not included along with the pet's name.
Paying hundreds of millions for a dread but getting a nightmare in the trade is why I would not buy an expensive pet near any building, thanks to those two kids teaching me a valuable lesson.
I think one excellent way to NOT be scammed when buying a rare pet is buy from the New Magincia pet stalls whenever possible.
Of course the devs maybe could consider gifting us with a true pet detection tool that gives the actual buff free base info of any pet we use it on, along with the breed and a warning if another pet with the same name is located nearby.