I spent 25 years in presales - the techie working with the sales folks. I have never seen a situation where a sales rep can price a deal at low margin without approval from a long way up the management chain. Salesfolks are often targeted just on revenue but the levels above them have a margin target as well.
I have on two occasions worked with sales reps who had recently joined from HP and were sueing HP for not paying commission. It's been standard practice there for a long time.