Yes, you can set your own markup on top of the supplier price. When you connect a flight API to your portal, you control what your customers pay. The API shows you a base price from the airline or supplier, and you decide how much commission or markup to add before that price appears to your customer on your portal. This lets you run your business the way you want and cover your costs and profit.
How you apply that markup depends on your portal setup. Some travel businesses add a fixed amount to every booking, others add a percentage, and some vary it by route or airline depending on their strategy. You can usually set different markups for different products, so your margin on flights might be different from your margin on hotels if that makes sense for your business.
Keep in mind that while you can set any price you want on your portal, you still need to be competitive so your customers actually book with you instead of going elsewhere. Also, some suppliers have rules about how you can display prices or what you can add on top, so check with your provider about any restrictions that might apply to your specific API connection. Talk to your glideFares contact about how markup and pricing rules work with the flight API you are planning to use.