Unless abused, I find it hard to believe they are so worn as to be considered potentially dangerous on a car merely 7yrs old. However, Section 2.4 of the MoT manual , especially the bits about missing/excessively damaged dust covers and 'excessive' play are pure joy for garages intent on maximising MoT income. These are usually the outfits offering cheapo MoTs and don't give a damn whether or not they will ever have your business again. Incidentally, a ball joint for Fiesta is about a tenner. Your story reeks of a rotten scam attempt.

If I were you, unless they really are knackered and you are rattling down the road, I would take it to a trusted indy - recommended by family or friend if you do not have one - and get it retested. If it passes, make a formal complaint to their head office saying you have been the victim of an attempted scam and demand your MoT fee back.

Drop a line to VOSA as well, they may then do a "mystery customer" on them when next in the area.