Would you be able to fit a change of clothes and wallet in this purse?

Even though this bag is very deep and wide, it's also very thin. A wallet will of course fit, but unless you mean infant clothes, it will be nearly impossible to stuff a change of clothes into this purse.

What are the dimensions of the purse?

Bag dimensions are 10” L x 2” W x 12” H. Drop is 23”

Is the strap long enough for a cross body bag?

The strap is very long and is adjustable, I had to adjust it to be shorter as I thought it was too long. I’m 5’6” for reference.

Is this bag authenic?

I can’t 100% answer this question of course but the quality is definitely up to par and it’s a great bag. I think the reason it’s less expensive is because the strap is not leather although when you look at the bag he really can’t tell because he can’t see detail I’m black I love it. Had it for months now.