Great and fair question to ask.
The commission agreement for the sale of your current property is negotiated between you and your Realtor.
The commission agreement for the purchase of your next property is not negotiated by you. It is, just as your was, negotiated between the listing agent and the seller.
Contrary to most people's perceptions, Realtors are not rich. A normal split between the employing broker and the Realtor is 30-50%. That means we earn 50-70%. After paying taxes, errors and omissions insurance, promotion, education, etc. most agents probably live on 25-30%.
The way to look at your question is really this: who is the best person to serve my needs? Only 35% of Realtors nationwide are full time. If your Realtor is in the few that dedicate their lives to working full time in Real Estate, are competent, good negotiators, and know their business, is it not worth it to go to sleep at night knowing that you are in good hands?