Property is worth the investment only if the return on rental income is 8% of purchase price or more. That is - if the cost of house is 50 lakhs - you must be getting a minimum rental of 32 K on it. However - you can lower rental threshold on purchase decision to 6% if property is likely to escalate by 10% in next years annually.
It is a sell call for a house if rental income for the property falls below 4% and price escalation lower than 6%. In case of an expected negative trend in house price - sell call is to be made.
Good theory - my wife does not agree. Too attached to "home"