What a cable does
A cable is a steel spring pushed down the line, usually with a cutting head on the end. It bores through whatever is blocking the pipe and restores flow. It is fast, it is cheap, and for a one-off blockage it is often exactly the right tool.
What a jetter does
A jetter puts water through the line at pressure and pulls it back along the pipe, cutting build-up off the wall and flushing it out. It cleans the pipe rather than making an opening in what is inside it.
The practical difference
Picture a pipe with a centimetre of grease coating the inside. A cable makes a hole through the grease. Water flows again, and the customer is satisfied. The grease is still there, and over the following weeks it closes the hole. A jetter removes the grease.
Which one you need
If the drain has blocked once and never before, a cable is usually enough and the cheaper option is the right one. If it keeps returning, the cable has been treating the symptom, and continuing to pay for it is the expensive choice over time.
What it costs you to get this wrong
Cabling is cheaper per visit. If a line needs jetting and gets cabled four times instead, four cheap visits cost more than one correct one, and the pipe spends the whole year mostly closed. The cheaper option is only cheaper when it is the right option.
How to tell which you are being sold
Ask what will be done about the pipe wall. If the answer is only about clearing the blockage, that is a cable job, and it is worth asking whether the blockage is the actual problem or the symptom of one.
Where each one struggles
A cable is close to useless against a wall coated evenly in scale, because there is nothing discrete for it to catch. A jetter is the wrong tool for a solid obstruction like a lodged object, and it is the wrong tool entirely for a pipe that has lost integrity.
What we would ask you on the phone
How many times it has happened, how long it takes to come back, and roughly when the house was built. Those three answers usually settle which of the two is appropriate before anyone gets in a van.