Well they are very sensitive. I had all but given up on them until recently. I had purchased 5 from different shops and none lived more than a month. I'm on my 6th now (ran into this beauty one day and just couldn't pass it up), and it is the healthiest specimen I've had so far. It's been six weeks so far, and it's vibrant and active in a way none of my previous ones were. The problem is breeding practices have weakened the fish, and the rams in the shops were bred at an incredibly low pH, usually around 5.5, so acclimating them to a significantly higher pH is asking a lot. If you can find a local breeder that has actually raised them in your local water, you will have a far greater chance at getting a specimen that can thrive in your water.
So, it's a little tricky to pick a so-called healthy specimen. They are fairly easy to sex though. Look at the black spot and if it has a blue sheen on it it's a female. If it's opaque it's a male.
If the risk is too great for you with the GBR's, go for bolivian rams. They are much hardier. While still beauties, IMO they just aren't as spectacular as the GBR's.