The real problem is if tenants, for some reasons, stop paying you
Other problem. Might be if he can't find tenants to Stay in the houses etc....
Property bubbles burst all the time and people are left kinda screwed
You suggest getting cheap properties which will then not be in prime rental locations so you may not have tenants a year around etc... Or you may have to reduce the rent if there are too many similar empty properties on the market....
A lot of variables to consider but if the house gets trashed by bad tenants, burglary, fire etc or they stop paying the rent and you live in another country are you going to fly across the world every time there's a problem or pay an agency a % of the rent to manage the tenant's?
Many things can eat into your profits