Had a transmission flush, was it a bad idea?

[xObLOwKISSESxO]

Today I went to Valvoline to get an oil change. They tried to sell me other stuff like a transmission flush and radiator flush. After much convincing and them telling me my transmission would soon seize without a flush, I did it. After reading about them I am starting to think this was a bad idea. I am a young girl and I feel like maybe they took advantage of my little knowledge of cars. My question is, will the flush make my transmission seize sooner. I have a 2000 Mitsubishi Galant with 107,000 miles on it. Was this a bad idea? I am freaking out because I don't have money to deal with any repairs. Also was the radiator flush good? The tranny fluid was dark brown almost black before they replaced it. Thanks so much to anyone who can help!
I read that pieces could have been moved around in the tranny which could block the wrong area causing failure and that the old fluid was safer, new fluid could shock the transmission.