1997 Pontiac Grand Am Questionable repair

The engine light had been on for several months, but we were told it was a sensor. The car stopped suddenly( would not boost), and a local mechanic replaced the alternator and battery, even though the battery was only 1 month old. The alternator had been replaced about a year prior. Three days later, it again died. They replaced the alternator again, saying it was defective, but the mechanic also stated that it was drawing alot of juice from the battery, but he did not investigate further. Less than 6 weeks later, the car again died, and would not respond to a boost. The CAA driver guessed it was the starter. I took it to a different garage, who did diagnostic testing, and had to replace a corroded alternator charging wire at the starter connection. We have had no trouble since.
Could that have been the whole problem from the start, especially since the first mechanic commented on the heavy pull on the battery? I feel the first mechanic ripped me off! Thanks!