Q: Dualboot Linux Manjaro and Mac OsX on Macbook Air

I just bought a macbook air with the understanding I could dualboot, Sales person at Apple said I could. I have found this difficult using Refind. Can anyone assist with this issue. Another choice is to setup an external HDD and be able to boot from this. If I can't acheive this I may put the device up for sale and take my losses and get other machine.