ISTPs are the opposite of aggressive when it comes to expressing their interest in a potential significant other. When gauging their interest do not look for words or verbal affirmation from them, as they will always be vague and dodgy and give you mixed signals. The ISTPs words will frequently if not always contradict what they did in the past. Instead, use your eyes and look for what they do, with you or to you (XD). As if they're making a word-less presentation of how much they care for and want you.I've always been aggressively chased by extroverts in the past hence that assumption. This is my first time encountering an ISTP so this is a completely different ballgame for me.
When this comprehensive presentation is translated into words, it is as follows:
"I want to be your significant other but will not say it, instead I will show it by sacrificing my own time out of my life in order to spend time with you, make and/or fix things for you, do things with you. Do not ask me if I want to be yours, instead please tell me you want to be mine."