Red Flag? Cash investor said seller to pay my assign fee?

[Autumn Allen]

Urgent! Is this OK or should I tell the cash buyer no deal unless you pay my assign fee. I worked really hard to find this awesome deal in a great neighborhood and cultivate relationship with the seller. Seller wants 190 and I originally offered 170, which includes 4K assign fee. One cash investor is willing to make a little less profit to bring the offer up to 180k, but said seller has to pay assign fee? I have never heard of this. Thoughts? Autumn A