New little dude/is kind of rude

So I just got this little guy, and I thought I was getting a deal/doing him a favor by getting him, as he was full grown and half off at the dumb pet store, which was my first mistake. I take him home, I set up his terrarium like decked out with everything and anything he could possibly need and not only did he bite me which I thought was rare for these guys, but he’s extremely spazzy and won’t even chill out when I’m putting water and food in there. Something tells me this guy has been returned before. I don’t want to do the same thing but having leopard geckos(and them being chill AF) I am not used to spazzy little geckos, especially getting bit. What should I do? Is there anyway to make him not bite or spaz when I’m giving him food and what not? And as far as feeding and humidity, it’s all perfect, hotter on top, mid hot on bottom, slightly cooler on the bottom, between 70 and 75 degrees, 70 humidity, and I have given him different crested foods and little crickets as well. What am I doing wrong? Halp