Usually when employers list a Flash developer/programmer (not designer) position dealing with flash based video games they do not clarify between Flex or Flash Pro. Based on your experience employers looking for flash devs prefer knowledge of Flash Pro or Flex? Although I realize you might reply both seldom have I seen it stated clear in various job posts. Thank you.

Just like companies are looking for C/C++, J2EE or .Net developers. Often, actual work that will be done involves none of the above.

The important thing to clear up in front is whether you're hired to do the code or are expected to do anything art-related.

However... No developer should be limited by the tools or frameworks. Flash indicates the general toolchain and line of work.

If any job specifically states "Foo Enterprise Pro 2.0 beta", it will be the lowest of bargain bin job. They will be looking for someone to keep the chair warm. These are tool operator jobs, not programming jobs. They will involve data entry or similar.

Someone applying for a Flash job should be familiar with:
- language (preferably at least last 2 iterations), such as AS2 and AS3 (I think that's what they are)
- toolchain (so I have this fancy IDE here, how do I actually deliver this to client)
- debugging and troubleshooting (how are plugins installed on different OSes, difference between debug and release plugins)
- testing (how do you make sure your stuff works? How do you test compatibility between different versions? Browsers? How to test it in VM)
- basic asset handling (how to convert images, sounds, applications to do so, common and supported formats, advantages and disadvantages)
- packages, third-party library integration, whatnot, don't really know, haven't done much flash-related stuff
- ability to set up a simple test server

Next, added value:
- which libraries, third-party packages, tools you have hands-on experience with (this is what raises salary/hourly rate)
- licensing issues, IP
- actual domain knowledge (how is Foo done best, which of Bar works best, what does Baz use and why)

The rest are likely generic skills, such as project management, issue tracking, version management, ...

I don't really think you need to worry about it.

Flex's main offering over Flash (aside from a better coding environment) is all of its UI component and application framework stuff, but I'd be really surprised if those features were ever called for or explicitly needed in flash gamedev.

Flash's main offering over Flex is the animation and vector tools, but if you're hired as a developer there's usually a decent chance you'll be working with artists who'll supply you with game assets anyway.

The main thing they are going to need you to have is strong, proven AS3 skill and experience. You can code a flash game in Flash itself, or in Flex, or FDT, or even use haxe and all sorts of other weird crap for bits of it.

Once you have the language experience, as an experienced developer you should be (and will be) comfortable building a game any way you need to.

As far as games go the two tools meet the same end, in my experience at least.

The key difference is that Flex is an actual semi-decent compiler, whereas Flash itself should not really be considered an acceptable tool for advanced AS3 coding if avoidable (you can use it, but why throw hours down the drain). It doesn't do much real error checking, it just believes whatever you say.

I work at a company that does a lot of Flash games, and we have about 8 or 9 AS3 developers here. We all use different tools. A few of us (including me) are using Flex - just as a compiler though, some are on FDT, FlashDevelop, etc... It doesn't really matter. I even occasionally do quick turn-around stuff just in Flash but only if no serious coding is required.

When replying to Flash job ads keep this in mind I guess:
- if they mention Flex explicitly, you may be required to have experience with its UI component framework. Otherwise, Flex is completely interchangeable with other actionscript compilers.
- if they mention Flash in general or just vaguely, or just say AS3, then chances are you'll be able to use any tool you want, or just use whatever compiler they have licenses for, and most of the time moving from one to another doesn't make any difference at all.