> Taking fees for lending but still, according to the Poloniex, a lender should be aware that the ability of the borrower to repay their loan is not guaranteed.

Here the ability of the borrower is defined by the set condition in the Poloniex engine which only recognizes the Maintenance margin and the collateral, and both are sufficient to guarantee that the recovery of the debt is mathematically possible. The maintenance margin is kept at 20%, so as to make sure that even during extremely volatile condition the position does not plunge into a negative balance, that will protect both margin traders and lenders. 

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