The ones I have hired to edit my writing - native speakers all, one a doctoral candidate in French literature to boot - have generally been mediocre at best. In the case of the native-speaker, doctoral candidate in literature (you would expect the best, right?) the text was completely mangled. She ended up with sentences that in English would read "The accused was convicted and hit with a 500 franc almond.", confusing the French words "amende" (a fine) and "amande" (an almond).
Funnily enough about 5 minutes ago I just finished correcting translations..for free* ( English to French) that had been done in a similar "interesting" ;-) manner, by "qualified professional translators" for someone..
They have a "bi-lingual" site, and wondered why the French were not enquiring ( inquiring - enquiring has already been the subject of lively threads here :) about their services and products..first time I looked at their site, I told them "I'm sorry, but it has so many errors in the translations, that anyone French would hit the back button..or laugh out loud", even the translator should have realised that the sentences make no sense when they read through their work in French..
However, the translator just trousered the money ( a lot ) and left the poor "rosbif" with a site to amuse the francophone gallery..some parts were also incredibly "wooden", using heavy and stilted formal business terminology, the sort of words not used in France for the last 50 years or so, totally unsuited to the subject of the site..( handicrafts instruction in small groups and things for very small kids to make )..the site code is horrid too, made in "word" with pages of thumbnails that are actually huge 5 meg jpegs "squashed" into 100 px "click to show larger image" bandwidth eaters..ackk!
That is the next thing to fix :)
* free because as Tom says..some you do for free..the site owner hasn't the money left to pay for corrections, and she gave me a very useful address of a supplier of materials that is only 60 kms from me, instead of 1200 kms further south..and I like the idea of what she does..:)
I agree with Tom and Lucy..if it is obvious ( make it so..give them the link to the Google translate button ) that you are giving them "auto-trans", it is better than nothing ..as far as French goes , Google is now better than Babylon or Systran ( even the most expensive versions of both ).but bear in mind, if you provide translations or links to translations, you will get emails etc enquiring about products or services in those languages, and auto-trans can get you into costly errors if you use it to carry on conversations..