What advice can anyone give about auctions? what is best to buy? at the moment i am just buying anything with 75+ rating with at least 1 win

Depends on your money, when you bet in the beginning on Black Caviar, you have enough money to buy every horse.

Buy every horse which has won a group race or 90+ mares for breeding.

Everyone probably has their own strategies when it comes to auctions. Strategy is influenced by the money you have, whether you are wanting to race only, or have an eye on the breeding barn. If the latter then clearly you are focused on getting mares. My approach is to buy horses that either have a reasonable rating or have raced in group races. Once purchased, I look at the absolute potential bar. If it is 80% plus then it is a definite keeper. But when you are starting you need to lower your sights initially, so you might start at 60% plus then work up from there as the calibre of your horses improve. If the potential bar is low then sell it and keep looking. The potential bar is not the only bar of significance, but I have found it by far the best guide when you are starting out. Another ploy I have found useful is to look for young horses that have only had 1 start, and see what the commentary says. If it says something like "ran green, will improve", then I buy them and check out the potential bar. You do get a lot of donkeys, but I have also picked up the occasional top horse at a bargain price.