Am I ruining my Wrangler's automatic transmission?

I took my 02 Jeep Wrangler Sport for a transmission flush two weeks ago at 34,000 miles. The mechanic I spoke to said he had the correct fluid for it (ATF +4), and the price was $120. About a week ago after doing some research, I got a bad feeling about the service...I got it at one of those quick oil change places. I found out that my Jeep was flushed and refilled with another type of transmission fluid mixed with additives that the mechanic said created ATF +4 fluid. The trans, actually, is shifting very smooth in and out of gear. But even though it seems to be functioning well, is it still possible that I'm causing damage to it? Should I just eat the cost and flush it again? Can this mechanic actually mix different trans fluid with additives to make it behave exactly like ATF +4? I appreciate any help and feedback.