If somebody doesn't bid on a stall then yeah... you can get it cheap!
Whether the system is good or not is debatable... but it sounds as though 'working as intended' from your post.
I got one in Craglorn once for 100 gold!
Maybe the normal guild in Rawlkha went somewhere else, or forgot to bid. Easily done. & with well established guilds its pretty normal for others not to contest the spot, leaving it empty if they do forget/move.
P.S. I presume you are in both of those trading guilds... and I'm sure neither of the GM's will thank you for posting their winning bids on the forums... I'd suggest taking them off the post and saying stuff like 'a lot more/less'.