The difference between が and を with the potential form of a verb?

Question

When using the potential form of a verb, I was taught that the particle を becomes が. However, in real life this seems to not always be the case. I've even heard Japanese people use を instead of が quite often. What's the difference between the following two sentences? Is を actually grammatically correct? ここで切符が買えますか？ ここで切符を買えますか？

Answer 1

Sure, you can use both. が is a topic marker so when you see が, you know what the main point of a sentence is.