They do get it wrong sometimes however.
My cousin has an Aussie G/F which he met here while she was on her 3rd Visitors visa.She did have another B/F from the UK before though and they split up.Her latest visitor visa had 3 weeks left on it when she returned back from Aussie land to see my cousin and because the ex B/F decided to make a call to the immigration they refused her entry.They said they had reason to believe she was going to overstay her visa even though she had a return ticket with Qantas on the expiry day of the visa and had a good job and a mortgage in Aussie land.Remember also this was her 3rd visa and she did not overstay OR break the rules even 1 time!!No appeal no rights,They stuck her on the next flight back.
It seems they really are tackling and over tackling immigration now
Positively shocking in my opinion and this only happened 3 weeks ago.