Does the Almighty's saying, "Hold to forgiveness," include accepting a service offered willingly and declining it if it burdens the one offering it?

The meaning you mentioned for taking the pardon is plausible, and do not hesitate to accept what is given as a gift; for people usually do not give something unless their souls permit it. If you are able to reward them, then do so, otherwise, it is sufficient for you to say to those who have shown kindness to you: "May Allah reward you with goodness," for the Messenger of Allah, peace and blessings be upon him, said: "Whoever does a favor for you, then reward him. If you do not find anything to reward him with, then supplicate for him until you see that you have repaid him," and "Whoever has a favor done for him and says to the doer: 'May Allah reward you with goodness,' has indeed exhausted the praise."