Having been working within the international property industry for years, I have seen many things, from ridiculous capital growth projections, sky high rental promises to plain unprofessional conduct.
The problem with any sort of prediction is you can´t really use previous years growth or performance to predict what you will get in the future ( I sound like my stockbroker now!). It is also worth noting that just because an agent tells you that property has inceased by over 20% this year, that doesn´t mean someone will walk in and pay 20% more. A property is only worth the price a buyer wants to pay for it. I always laugh when I hear "on paper its now worth x amount".
My favourite, though has always been the valuation process undertaken by some agents.
Some familiar dialogue
Client : So, Mr. Real Estate Agent, I want to sell my property, what price would you suggest?
Real Estate Agent : How much do you want for it?
Client : Well, I was very much hoping that you could give me an idea.
Real Estate Agent : Yes but, how much do you want for it?
A good agent will give you solid examples, he will show comparisons of similar properties in the region, if your property is in a development then he will know it like the back of his hand.
Although in reality it is a far less exact science than back in the UK or USA, there is still enough information around to give good advice on price and sales strategy.
But remember, do your market research too and get a few valuations before you decide on what price is right.