Hi! Would it be possible to write a script so that during sales order entry, the list of items that are most frequently purchased by each customer are highlighted?

It is possible, however this is going to requiere a customization outside the standard NetSuite API to build or modify the item selection popup on the fly. You can probably get away with a custom sublist field to select the item that is populates from a custom search but still the highlight portion of it is going to requiere some non-standard customization.

Thank you!