I can only speak to Avianca...this is 100% true. Only it's not that hard.
If you go on their site, it'll geolocate you and adjust. Change the webpage to "Colombia" (and I swear) Spanish, the prices drop SIGNIFICANTLY, at least for domestic flights.
There was a time where you had to "reserve" the ticket, then call them and pay with your Canadian/USA credit card. Then they kinda squashed that. There was a stretch there where the website wouldn't accept my Canadian card, not sure if it was the brand of card or what. But it's back to working. For the last year plus, I just change it to Colombia/Spanish and no problem...pay with my canadian card.