There are many ways of explaining/thinking about this truly brain bending riddle! It all boils down to the fact that the lawyers's math is incorrect.

They did NOT spend $9 • 3 + $2.

They spent exactly $27 dollars. $25 for the room and $2 for the tip. Remember they got exactly $3, in total back.

Another way to think about the answer to this riddle is to just pretend that the bellhop refunded $3 to the lawyers (rather than giving them $5 and receiving $2 back).

If the lawyers get $3 back and each takes $1. They they spent exactly $27 dollars.