Does anyone have any suggestions on verifying an item on a sales order exists before creating the actual sales order? I am currently working with the RESTful APIs available for 2020.1. TIA!

recommended way is to use an external id in combination with the upsert operation

I don't think upsert will work for my use case. If the item doesn't exist then I need to send it through with a specified 'non-stock' item number. I'm not sure queries are efficient enough either, and might result in a relatively high amount of queries. Thanks!

This sounds like a good use case for a Restlet script ... you can run various searches and make dynamic decisions in the restlet script, all from a single web service call.

you might be able to combine a bunch of your item queries by using the OR operator

using the lookupfield API is better than a search form a perf point of view.

I'm trying to do as much as possible without custom coding within NetSuite itself. But I do appreciate all the feedback and suggestions!