You just tell him that you think they wouldn't make a good match because you think that he's too perfect

What do you mean by too perfect? If he thinks you're good enough, then why don't you? But if it's not a self-esteem issue, then tell him that you value his friendship (I'm assuming you do), but you're not interested in a romantic relationship. Honesty (though not of the brutal variety) is the best policy. Basically, think what you'd like to hear if the tables were turned.

It's hard to figure out exactly what you mean by 'too perfect', but I know that with some men life is just too easy, and for 'easy, read boring! If you feel like he ticks all the boxes, but just doesn't do it for, just tell him that you think getting together would be a bad idea, as you just dont' feel like you're suited to each other.

Honey, there is no such thing as a perfect guy! There is a flaw somewhere, believe me! If u are not really into this guy, tell him that a friendship at this stage would be better & see how it goes from there. You may just realize that he may not be perfect, but he is perfect for you! Good luck