An estimate is a rough calculation of what a job will cost, which may change in the end depending on what is found or how long it takes. It gives you an idea, but it does not commit to a set price.
It is used when the tradesperson has not seen the job or does not have enough information. The risk is that the final figure is quite different from the one you were told, and in an emergency you no longer have room to look for another option.
That is why it is better to ask for a fixed quote. We give one before we start; a photo of the door and the lock on WhatsApp is usually enough. If, once we check on site, the job changes, we tell you and do not carry on until you are happy. For communities of owners and businesses, we cover it under lock maintenance.