Probably not really a big secret as you might thought since it's information they can also access if they really wanted to from other means. The right move there was telling them the truth than sow distrust over petty fees. Yes, you earned a competition from that but it's not like your service as a business can be secured as you being the only capable provider. It's still a competition of convenience now and how much the end users are willing to pay for convenience.
I had the same setup when I was studying but the difference in people knowing I charge higher than the competition is that I'm constantly unbothered whether there is a customer or not since I'm doing other side hustles, playing the same game but simultaneously on different fields. And it's not always a guarantee that the competition will always be conveniently available. Sometimes people just accept my rates because they get instant gratification a few hours earlier than wait for the competition to be available in a few hours and this at a price difference of 10 pesos (figuratively).
yep it's really not a secret especially for those people who will make an effort researching but the real customers who doesn't just pay higher.
Just like for example, for buying load of my customers, I also avoid using Gcash as I need to pay for fees (Gcash gets 1%-2%). I use Seabank instead and get 3% discount + 5-peso fee from my customer. I only use the former if the promo is not available from the latter haha.