Here is an excerpt of the Legal aspects of free and open source software workshop notes. Every phrase is a masterpiece.
"When the public agency has decided that open source requirements are particularly important for a specific software acquisition case, the process described in this section can be followed. This process would end in the agency downloading open source software itself, with no fee paid whatsoever. Separately, commercially provided services and support, if required, may be acquired by publishing calls for tender. Note that this process can be abandoned at any point - for instance, if the software cannot be found easily, or evaluated, or once downloaded is found unsuitable for any reason. At that point, the other approach described in the next section can be followed, namely, publishing a call for tender for open source software."