What can happen if my friend got caught selling drugs to an undercover and it was his third time when they finally arrested him?

If he is charged in a Michigan state court, and the drug is marijuana, the maximum is 4 years. If the drug is a common pharmaceutical or other illegal substance (heroin, cocaine, oxycodone, hydrocodone, etc) it is a 20 year maximum. I do not know whether he has a reasonable chance of winning at a trial. If he is not convicted, he will not receive any sentence. If he is sentenced, either after a trial or a guilty plea, he and the attorney need to carefully go over the pre-sentence report and the sentencing guidelines scoring, and possibly get letters of support from respected members of the community. If he has a previous record that presents additional complications. Whether he gets jail time depends largely on which drug, the amount of the drug, the past criminal record, the sentencing guidelines scoring, what the defendant says at sentencing, and the attitude of the sentencing judge. No lawyer, no matter how great, can guarantee a particular result in this case.

Anything is possible with the right attorney.