How to adjust a boat trailer?

[steplift20]

My son ( a chip of the old block) has a 2003 19 polar no matter what he does he can't get the boat to center itself on the trailer, when he first bought the boat it went on straight than a tree fell on his boat and broke the console, he got it fixed but now the boat never goes on the trailer straight. The trailer looks straight and not bent the boat looks fine too , what gives? What should he look for? We tried moving the rollers in than out , nothing still the same. I'm asking for your views to this issue. He wants to buy a new trailer but what if it still goes on crooked than he is out $3000
Maybe this happened to someone else and what did you do
Thanks