A negative freeroll is relatively common in low stakes amateur play, but in higher stakes play, it is considered a serious blunder to  allow a negative freeroll on the final round of betting due to the amount of risk involved.
Allowing a disadvantageous freeroll is typical in low-stakes recreational play, however, in high-stakes games, it is viewed as a critical mistake to permit a negative freeroll during the final betting round because of the considerable danger entailed.