If someone has an investment property that they need to close in the 9 days, otherwise they will lose the property and the deposit on the property. Is that allowed?
When there would be a substantial loss involved otherwise, you may close the investment property deal during the nine days. This is especially the case if this is you do this for a livelihood. If it would be possible to delay the deal for a small extra fee, this is praiseworthy.
Shulchan Aruch (Orach Chaim 551:2) & Mishna Berurah 11 -12.