Here's the perspective of aa music store owner, and sometime guitar teacher.
If you learn to play southpaw instruments, you're at a 99% disadvantage for buying instruments and trading unstruments. For every 1000 righties made, there might be one or two lefties.

There are instructional materials just for lefties: books, tapes, DVDs, etc.

Get the teacher to face a mirror, with the student mimicing the reflection: eureka, instant leftie instructor!!!!

Wilco in Tennessee