can a company charge gst after advertising proce?

In Australia, if you advertise a price to consumers, it must already include GST — tacking on an extra 10% at checkout is a cheeky surprise, not a legal one. The only time you can slap GST on top is when the ad clearly says "ex‑GST" or "plus GST" and it’s genuinely aimed at business buyers. If a single price is shown without that caveat, charging extra GST later can run you afoul of Australian Consumer Law for misleading pricing. Online or in-store, delivery can be extra if disclosed, but the product’s advertised price itself should be GST‑inclusive. If there’s a genuine typo, fix the ad, don’t ambush the customer post‑agreement. For chapter-and-verse, check ACCC guidance or get proper advice.