I was looking to buy an air conditioner (split system), recently and a local dealer told to go for ACs with cooling feature only and not ACs with heating feature, as they require more servicing and consumer faces many problems with them. I couldn't find anything validating this online. Is this true?
It's not clear if you're talking about mini-split AC systems with a heat pump or window AC units with resistive heating. If you mean the former, those systems are becoming more popular and are a very efficient way to heat your house, especially if your climate stays within the external temperature range supported by the unit (down to 20 or 30 ºF in older units, down to 0 ºF or less in newer ones).
On the other hand the window units with resistive heating is probably not worth your time, they are inefficient and you are probably better of removing the unit from the window when it gets cold and getting a space heater.
The biggest difference between them is that reversible AC has an extra 4-way valve to reverse the flow. That's not a very fragile component. The seller might be either talking from his personal experience that's particular to one make or series, or he might be simply employing FUD in order to convince you into purchasing item with higher profit margin for him (most likely imho).
On the other hand, it's quite easy to ruin the unit by keeping it on as outside temp falls too low. The heating is designed to be only an accessory method ran occasionally on chilly summer days and not to replace a furnace in the winter (that's what big heat pumps are for). He might be simply trying to avoid future problems with careless customers who fail to adhere to manual.