I kinda have a similar problem but I feel the regret after I have purchased something. When I’m uncertain about buying something or when I’m totally certain but someone tells me otherwise, I just can’t get over the guilt. For instance, I joined a training course at the beginning of the year and when I did, I felt like I paid a fair price for the courses that I opted for. I started my classes and one of the guys there told me how his friend paid a lot less for a similar course (similar, not the same). Since then, I haven’t been over the guilt and I even called the company yesterday to demand a refund only to be told that the company has a no-refund policy! 🙁

When I try thinking about why I feel the regret, it is usually because I end up feeling wronged, as if someone blatantly cheated/robbed me and hurt my self-esteem/ego and how I couldn’t do anything about it. It can happen for things ranging from petty prices to costlier stuff.

So just know that you are not alone in your misery.