Ink after wash doesnt look as crisp

Hey Margino,
The first thing I would do is refer it (or get) the product information sheet about the inks. You need to check that you are achieving the cure temp of the ink.
To cure the ink it is not about just applying heat, the ink itself has to hit a certain temp.
When you ironing them is it a slow iron, on the hottest setting the fabric can take with no steam or water spray. I would also recommend that you don't iron directly onto the print, but place a bit of thin cotton over the image area.
You should also be able to bake them in an oven (not gas), but the temp and dwell time should be on the info sheets.
It sounds like the best place to start as the variation is presenting after you wash you garment.
If that doesn't fix it, go to your local art supply shop and buy the smallest container of a different brand of ink, test it.
If you find the same think is happening then it maybe something in your process, if not then it maybe the ink.
Let me know how you go.

Buy a flash cure. Your shirts may not fade after one or even two test washes but they will eventually.

You are planning on selling the shirts so best to do it right the first time. You could be doing potential damage to whatever business you build over the coming year(s) with shirts that wash out.