Conspiracy drug charges or hear say?

in virginia federal court can a person be found guilty of conspiracy to sell drugs just on the testimony of a informant alone. no drugs seized, no money, no cars, no houses, no evidence at all. just a guy that says that this person sold them over 400 kilos over a certian amount of time. and to top it all off, the informant was caught with drugs so he is trying to get a lesser sentence by coming up with this hear say story .is this legal? can the federal courts find this guy guilty of selling 400 kilos when they dont have no drugs from him, no vedio, no audio, no money, no cars, no houses, he cant even afford to make bail or even hire a real lawyer. and thats all they have is a guy looking to get a lesser jail sentence by saying that this guy sold him 400 kilos a little a atime over a year or so. if so our judicial system is a joke.