I am searching TransactionLine using SuiteQl and the "quantity" field is consistently returning the value as a negative number. Why is this so and how could I get the correct value?

I'm not that familiar with Suiteql, but I know in saved searches, that will depend on what transaction type you're looking at. A fulfillment for instance will usually have negatives since it's stock going out the door. An item receipt will have positives since that's stock coming in the door. Maybe transaction type is your issue?