I would try the following:

Remove derailleur and clean.
Lubricate all pivot points. If it shifts ok going to the small ring then the spring should be fine.
Replace shift cables and housing
Reinstall based on these criteria:
Front Derailleur Adjustment | Park Tool

Do you have pictures of your bike and specifically the chainrings/derailleur? Could the inner cage be bent and that's why the bike shifts well to the inside but not the outside? I'm thinking if a mechanic couldn't get a relatively simple system like a friction front derailleur to shift well then the derailleur may be damaged.