Every morning this import system is executed. Each property saves its incoming data. In the next execution, system will compare current execution data with the previous saved execution data. It detects changes by fields:

As an example, in the agency change any value in their source (inmoba, Infocasa, etc), in the next execution will detect that change and it will force an update in that field (and it might provoke changes in other relative fields).

If agency changes price value (for example), in the next execution price will change in Resales-Online, but if price is changed it should update some more relative fields as commissions.