Guarantee and repair scams.

With rental and guarantee work, there is no money to be made by the shop - there is only the cost of the work or replacement. If they just tell you, "no guarantee, no repair", Trading Standards can jump on them from a great height.
So they must make you believe that you have no claim on them, that there is nothing wrong with the equipment in question.. "it's your aerial Madam" often works fine.
I have also heard this used to avoid fixing problems caused by the initial repair not being done right.

To repair a product takes time and parts, selling a new item is a quick exchange of goods for money. Often, it can be much more profitable for them to just sell you a new one. Not that they wouldn't make money on a repair, just that they can make even more if they can convince you to buy a new one.

Many salesmen and dodgy repair people will drop in the odd technical term to impress the hell out of the customer. The chances are that they don't really understand it, they are just dropping in words they have heard.

Sometimes a salesman or engineer may come across a customer who disputes the rather high repair charge or claim that a new one is needed. This is where the impressive test equipment and workshop claim comes in useful. The wording may go something like, "we have a large workshop and £1000s of test equipment, which cannot be wrong". The very wording of their claim shows their lack of knowledge.
Test equipment can be wrong: it must be regularly calibrated in a proper lab to ensure accuracy.
The equipment does not state what is wrong: the engineer decides that from the readings. The engineer can be wrong.
Most CB repair places have very little test equipment. Unfortunately, CB repairs do not pay enough for such equipment. Unless the shop also repair more expensive equipment, they will not be able to afford such test equipment and regular calibration.
I have heard the large workshop and test equipment claim from a shop who I knew to be doing their repairs in a cupboard under the stairs (around 6'x2') with less test equipment than many CB users. What little they had was outdated or broken, but the customers never needed to know that.