Although I have not been able to Ebay lately, I took the time to read some reviews on counterfeit flea medications tonight - particularly Frontline and Advantage. There are those of us who have sold/sell these products and they are legitimate, non-counterfeit products. I have also realized that many of the persons writing the reviews, have very little understanding of how these products actually work. Here is my best attempt at explaining the differences.

First. if you have ANY question regarding the legitimacy of the product, you should visit the manufacturer's website. Meriel, (who produces Frontline and Frontline Plus), has a webpage describing the appearance of legitimate from counterfeit products. Advantage (produced by Bayer) also has a similar page. Both of these products, if the product is used and made properly (not counterfeit), DO NOT absorb into the pets body - it remains in the oil glands of the skin and can last up to a whole month if applied properly.

Although, Frontline is labeled as waterproof, it becomes less effective if the animal is bathed often - since the oils from the skin are being removed with every bath. If you have to bath your pet, use a SOAP FREE shampoo, that will not strip the oils from the skin. Advantage works in a similar fashion as Frontline, but it has no effectiveness against ticks. Neither of the products can work well in a heavily infested area. For every live flea that you see, there are approximately 1 MILLION FLEA EGGS in the environment. The environment often needs to be treated in addition to EVERY animal in the house if the problem is to be eliminated.

Another reason fleas can be so difficult to eliminate, is that in the egg stage, they can survive for 6 months without feeding. Often owners think they have the problem eliminated when the eggs finally hatch and you are back to step 1 - especially if you are not using flea control year round.

The products often mentioned that are sold at large department stores,  usually do not work and they can cause some SEVERE health side effects. For instance, many of the non-veterinary products can be adsorbed into the blood stream, cross the blood brain barrier, and lead to seizures and possibly death.  These medications do NOT stay "outside" the body in the oil glands. Alos, if an owner accidentally applies a dog dose to a cat, it can be deadly.

Advantix is labeled for dogs ONLY, as it can be lethal to cats. Revolution, which should not be sold on Ebay, is a prescription product that protects cats and dogs against numerous parasites, including Heartworm Disease. If you are interested in Revolution, please visit Pfizer Animal Health on the internet, and purchase it from your Veterinarian. 

I hope this review helps. Please direct further questions to a trusted source - like your family veterinarian or the companies who manufacture the products. Good Luck - fleas have been horrible this year!