Pearl, I noticed your status says you are from Perth and the IP is in Melb. Did you and your sis live in MElb before you bought the property?
When you bought the property, did you have a look around and do a bit of research, and did you both consider the price to be reasonable at the time hence you bought it?
HOw much do YOU and YOUR SIS think the property is worth now? Have you checked the prices in the area? I assume you probably paid similar price as others who have bought the property in the same building ... so they must have thought it was worth it then .... I'm a little bit shocked at how much lower the CBA valuation is, has the area dropped significantly and if so for what reasons?
THe bank valuer is not always spot on. THe professional valuers don't specialise in the area and use 'comparables' which may not have sold at arms' length etc. Whilst real estate agents working in the area are not professional valuers, they are likely to have a better idea of how much the property can be sold for. I would suggest you call around a few agents in the area right away, tell them about the property and tell them you have bought it but thinking of offloading it as soon as the sale is completed. That way they might think you could be a potential vendor/customer and would be willing to offer you their 2 cents. Tell them at the outset you have personal reasons for selling the property and hence you want a REALISTIC figure and a QUICK SELL (that would discourage them from just giving you a high figure hoping you would take your business to them instead of someone else). Get a few different verbal 'appraisals' and compare them with CBA's valuation. If CBA's appears too low, start making inquiries with other lenders immediately, try brokers who may have access to different lenders that may be prepared to lend you and have different valuers who may value the property higher than CBA.
If this still doesnt work out, then we can worry about the builder suing you for the difference.
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By the way I don't mean to question the ability of professional valuers ... but in my experience, the REAs can hit the mark a bit closer.
Professional valuers value how much the property is WORTH based on comparables in the area. A local REA can tell you how much they think people looking for properties in the area are prepared to pay for your property. They can be two different figures.
I do a lot of research before I buy a property, personally as opposed to getting someone else to do it, and I generally keep myself updated on the area's performance so I can provide a fair estimate of how much the property is worth at any point.
When I refinanced my last property, the bank valued it about 5% more than what I thought it would sell for. This is probably because that house was the 'worst' on the street. It obviously worked in my favour as it created more equity for me. About a month after, my property manager did a routine inspection and dragged along a sales person who provided a free appraisal. His range was almost identical to the one I had in mind. I think the valuer wasn't that far off and it was good to know he thought my property was worth that money - which it is, but given the market was starting to cool, I had reservations as to whether people would be prepared to pay for the price valued by the valuer.