When buying a tool...

...or pretty much anything to bring into your group there are some basic things to consider.  Now most of this can be found in many of the automation books out there, or in the QA Forums if you search for it, but I wanted to put down my own personal checklist.

1. Consider who is going to use the tool - if its just you, and only ever you, then whatever fits your skillset is fine.  If other people are going to use this, not everyone will have the same experience, and some people like using detail-driven tools, others do not.  Make sure it fits the audience.
2. Don't go for whizz-bang cool stuff - there is always a hot tool out there but it may not be a fit.  Picking something just because it looks cool, or is going to be resume fodder, is not the way to make a wise decision.  Go for a tool that works, not a tool that sounds neat.
3. Make sure it fits the project - not every tool is simple and easy to use, in the midst of a project bringing in a tool that requires a lot of focus and start-up time, such as training and installation, is not wise.
4. Plan for future needs - again, focusing on the here and now is fine to get you through the immediate needs, but at some point all you end up with is a bunch of tools that get you through a defined set of problems.  Thinking ahead, what will be other platforms that will be supported, other technologies coming in the next project, all of this should be taken under consideration.
5. Do a demo - take a small subset of what will work and run a prototype, or a demo of the tool.  Open Source projects can be used at any time without issue, but if its a commercial product see if they will allow you to demo it against your tool yourself, many will give you 30 days or so to check things out.  If you build your own, do small prototypes that you can expand on or gain the knowledge you need to be able to do full builds.
6. Check more than one tool - don't decide on the first one that works, do some due diligence.  This is the hard part, because it often when you find one that looks like its the best thing ever, and will do everything you want its good to take off.  Do your research and check every item on your list, sometimes you will come up with more than one, then its a matter of what will fit the team, environment and needs.  You can often end up with a better candidate this way.
7. Talk to people - while we all have our own ideas of what the needs are, others who may need to use the tool will also have requirements.  Sometimes something at the back of their minds that is hard to use, or do or something that would make work easier, get all these items into a requirements list and document them.

A lot of these steps are important in one critical step, the rationale behind why the tool is needed and why it will work, you never want to be stopped by someone who says "Well why do we need this new thing if the old one works?".  You should have the information at your fingertips to say, "oh, that's because we can do A and not have to worry about B and C..."

If you can't talk about why the change will help, then you haven't done your work.