As a prospective buyer of a house or apartment we might feel entitled to check out a property thoroughly at an open for inspection, or ask the agent anything that we feel we need an answer to.

After all, a home purchase is the biggest financial outlay in our lives for most of us, so it’s all part of due diligence, right?

Why shouldn’t we turn on the shower full-blast to check the water pressure, fling open the cupboards to test their sturdiness, flick the light switches on and off to sniff out any electrical problems, or flick out our smartphone to takes a snap of anything we find interesting?

Well, it depends. Although we should have reasonable expectations that our questions will be answered by taking a look at a property and quizzing the vendor’s agents, there are some behaviours that are absolutely unacceptable.

Arch Staver, a director of real estate agency Nelson Alexander, has been showing, auctioning and selling houses in Melbourne’s inner-north for 28 years. And he says he’s seen a thing or two that he’d prefer not to see again.

“The height of rudeness and what’s very discourteous to the vendor and agent is for the prospective buyer to loudly announce they don’t like the house at an open for inspection. It’s a very distasteful thing to do,” Mr Staver says.

“If they don’t like the house they should say ‘no, it’s not for me’ and quietly leave.”

Really? Isn’t that a little over-sensitive?

Mr Staver says while feedback is welcome, loud and aggressive negativity, especially in front of other potential buyers, is not. It has even prompted him to ask such people to leave the property.

Breaches of inspection etiquette also include opening cabinets and cupboards that are not part of the sale, flicking through the owner’s photo albums or reading their bills.

Believe it or not, such things do happen, and more often than you would think.

“You’d be quite surprised,” says Mr Staver, who has more than once had to tell a prospective buyer that an open for inspection is not a free pass to do as you please.

If a buyer needs to use the bathroom then that is acceptable, but please don’t pull out your phone and snap away without first asking the agent for permission.

Mr Staver also doesn’t approve of potential buyers bringing a building expert to assess the property during an open house.

“That should be arranged for a separate appointment,” he says.

An auction can also be a minefield of bad behaviour, with stickybeaks poking about or jokers driving by yelling insults.

“That’s just part of the whole experience,” he says.

But sometimes things can get out of hand.

“I once sold a house in West Melbourne for a vendor who had had issues with a neighbour about noise from his pub. The publican wore a sandwich board during the auction listing all the things wrong with the house. He also used a loudspeaker,” he says.

The angry neighbour succeeded in halting the auction and Mr Staver took the prospective buyers into the house to privately negotiate a sale.

The states have rules and regulations for out-of-line real estate behaviour, which could lead to stiff fines or punishments. But Mr Staver says there is so much disclosure about houses that is required these days that bully boy antics are now infrequent.

He does, however, advise prospective buyers to always do one thing when inspecting.

“If it’s a house you really want, go to as many open for inspections as you can to see how many others are really interested.”