A bag can be cheap to buy and expensive to keep useful. The zip is worth examining because a small missing pull and a damaged zip track are very different repair problems.
Before buying a used bag, empty it with the seller’s permission and open every compartment. Move the zip gently through its full travel. Look for missing teeth, torn tape, a slider that separates the closed section and lining caught in the mechanism. Do not force a stuck zip to prove that it works.
Identify the fault before pricing the repair
A missing pull may need a simple suitable replacement. A damaged slider, tape or chain may require a different part or more involved work. Access matters too: a zip sewn into a complicated lining can take more labour than one in a straightforward pouch.
Ask a repairer what would need replacing, whether a compatible part is available and what the complete repair would cost. Provide clear photographs if the repairer accepts remote enquiries, but understand that a firm assessment may require seeing the bag.
For a fictional comparison, a 15-unit bag needing a 30-unit repair is not automatically a bad purchase. Its condition, usefulness and alternatives matter. But it is a 45-unit decision, not a 15-unit bargain. Include travel or postage if those costs are necessary.
Check the rest of the bag
Inspect handles, attachment points, seams and the base. Repairing a zip may make little sense if the surrounding material is disintegrating. Conversely, a sound bag with one repairable fault may remain useful for a long time.
Avoid applying random oils or household chemicals to the zip; they can stain fabric or affect finishes. Use the maker’s care advice or a competent repairer’s recommendation.
Keep a note of the replacement part or repair performed. Next time, you will be comparing a known, usable item with a new purchase, rather than replacing it because one small component became inconvenient.