I've been doing a/c repair for many years.
And,I agree,the phrase-"Just needs some freon" is the most common complaint I hear!
If it needs freon,it has a leak!
Leaks cost time and money to repair.
One can won't fix it!Ever!It will still leak.
And,usually,it's a waste of time and freon.
But,it can get very expensive to rebuild a system,so most just sell the car and buy one with working a/c.
Or, do without.
Mike.