I buy directly from Thomas labs. You can buy on Amazon or you can buy Safeguard Solution of fenbendazole at a farm store. Also the horse paste.
I assure you it tastes terrible in all forms. The safeguard being the worst. I can't get it down but the dogs don't seem to notice. The cats and I prefer the granular. I use the horse paste Panacur because it has sweetener added and it is the best value when using high doses.
I'm not saying yours is not fenbendazole but that is something I would never buy on e-bay.
Is yours sealed in white aluminum foil packets with name and date code applied? If it's in plastic bags it's probably sugar.
The packets are 250 mg coming from Thomas Labs. they contain about an 1/8 of a tsp.