When I see it on TF2 wiki, I could only find info about its disadvantages from missing people. What makes the Bazaar Bargain so good that I would rather pick that than the stock sniper?
Bazaar Bargain is one of those items that just depend on your playstyle and skill.If you keep running around getting one-two headshots and then die it is pretty much useless to you,but if you keep getting in good positions with nice headshots and killstreaks you will have a nice bonus without even noticing the disadvantage.
The -40% starting charge rate sounds like a big disadvantage,but really it is not.It just means that after you set up in a nice position you will have to wait 4.6 seconds before the first shot instead the 3.3s , which is negligible considering the benefit.
Now if you ignore the starting charge,you can see on this graph the benefits. You can also ignore Huntsman since it is more of a mid-range weapon due the high projectile drop.
Also note that the graph ignores the de-buff of the bazaar for the first shot completely,meaning that the charge time for 0 heads is actually 4.6s but rest of the values stay the same.
And before July 10th the starting charge rate was -20% which was like 0.8s,really negligible.