I paid 25 bucks each to have each one flow tested, sonic cleaned, new filter installed, then re flow tested. Made a huge difference in the fuel economy on car they were for as 2 of the injectors were flowing about 25 percent less then they should have been.
The actual flow testing test is pretty simple and is fully described in the FSRM, but you need a couple special items. One is a SST that is just a resister to hook up between +12v, unfortuantly it doesn't say the resistence of the SST. And you will need a graduated cylinder and some hose and such. You can also buy the filters directly from a fuel injection shop and change them yourself but you still won't be able to replicate the sonic bath, but you might be do ok with some injector cleaner or intake manifold cleaner and the SST or home made version.