Wait until economy and property market turns down.
The sucker loses his/her job, got no money to service the loan repayment on the first property.
The rent on the second property drops, insufficient to cover the loan repayment or, even worse, there is no tenant and the second property is earning zero with loan repayment. The bank repossesses and sells the property; usually at a time when the economy and the property market is bottoming.
The sucker cries his/her heart out when the economy and the property market recovers and see how the property price recovers.