I am outsourcing a couple of jobs, involving C#, javascript, MS SQL Server. How can best assess a providers skills? Online, and even offline, people can say anything and often do. Are there any questions I can ask to determine their skills? I've asked a programmer friend to do this, though he seems capable though too busy.

For example, if someone was looking for a mech. engineer (my field), for a particular job, I'd be able to suggest questions to ensure he/she at least is likely to have the relevant skill set.

Does the same apply for programmers. I'd be grateful for any other solutions to this issue. Can I contract someone to actually assess skillets?

Thank you in advance for any help.