"You have an error in your SQL syntax; check the manual
that corresponds to your MySQL server version for the
right syntax to use near '\'' at line 1"
As soon as we see an error message like this, we know we can dump the entire database in a matter of minutes.These days, we usually have to work a bit harder to find the more difficult to identify and exploit SQLi (e.g. boolean-based blind and time based) but the end result is the same once we do. SQLMap is a standard tool in a any good web app penetration tester's toolkit. It's not always going to work but when it does it automates away a lot of the grunt work. I applaud the SQLMap developers who seem to know SQL inside out and actively acknowledge feedback from the community.
For any devs, this is decent guide for preventing SQLi:
https://www.owasp.org/index.php/SQL_Injection_Prevention_Che...
I would say that SQLmap is normally effective at determining whether a HTTP parameter is injectable with a high degree of confidence. However, sometimes there will be Web Application Firewall (WAF) filters or unusual/inconsistent application behaviour on certain inputs which means it can't confirm whether the parameter is definitely vulnerable or not (less than 10% of the time in my experience). For the same reasons, often it won't be able to successfully automate the exploitation for you. On those occasions, we have to craft our queries manually to exfiltrate database contents and so forth.