The defendant needs a good criminal defense attorney ASAP. The police frequently use a confidential informant to work off their charges by setting up other drug consumers (buyers and sellers). If the police have a live witness, copies of the audio recording, the money and/or drugs, third party police officers monitoring, etc., certainly a charged defendant can be found guilty of a criminal drug transaction. This is classic police work in drug crimes. The defendant needs a good lawyer ASAP.
I am trying to give you a general answer to your question. We do not have an attorney-client relationship by this response on the avvo website. I have not been retained to represent you. I am licensed to practice law in Kentucky and in federal court in this state and the Southern District of Indiana. You need to seek legal advice from an attorney licensed to practice in your area..
Very often drug charges are based on controlled buys using a confidential informant, so this is not uncommon. However, there are numerous issues related to use of CI's for controlled buys, so you should contact an experienced criminal defense attorney.
The facts you state are enough, absolutely. But your question had another component. You asked is it enough to convict for the charge with a prior conviction. The prior conviction must be alleged and it operates as a sentencing enhancement. The prosecution has to prove that conviction with competent evidence, as well.