first, if you have your buyers list ready BEFORE you contract a property, you will have an advantage. because if you take an investor to the property early in your contract, he has to wait a month or two if he wants to go around you. and if he seems shady you can try to match another buyer before the 1st idiot can go around your back.
you are going to find people like this everywhere, its a result of the bottom-line thinking that is becoming so popular in america. everyone wants to cut out anyone who is perceived as a "middleman." but the important key is, is this person adding value? if not, then i agree, they should be cut out of the equation.
if you are a decent wholesaler, you are bringing deals to investors who may not have time to find their own property, or lack the drive/skills to find decent properties, or are afraid to set foot in the ghetto where some of these deals are located, etc.
if someone gave me that line, i would just write them off in my head because obviously he is close-minded. the question of whether you make an assignment fee is irrelevant; his only concern should be how much profit does he stand to make? pure and simple.
if you went to two different car dealerships and found the same car for the same price, then you found out that one of the salesmen was making a higher commission, should you care? you probably want to, kind of, because you are letting your emotions manipulate you, but what you SHOULD be thinking is that if the end price you pay is the same, it does not matter.
another way you may be adding value to the transaction is by negotiation; who knows, you may be getting a better price out of the seller. suppose the investor went to the seller and got the price down to 60. if you can get the price down to 50, even if you take a 7500 assignment you still made the investor more money.
in the future, however, i wouldn't blatantly dump it on them that you are a wholesaler. i would talk to them about a property, see if they are interested, and then when it eventually surfaces that you just have a contract on it, if he raises questions about that then just say "if you think it's a great deal what difference does it make whether it's wholesale?" if the numbers work, he shouldn't care. good investors are not quibbling over who made what cut, they are thinking about how can they possibly squeeze more deals out of each month and make more money.
if you start talking about a property with someone and they jump all over you about "are you a wholesaler" or "are you just going to assign this" i wouldn't waste your time with them, those people are too dense and it's not worth spinning your wheels trying to convince them to do business. they will be a pain in the *** every step of the way. focus on finding people who want you to make them more money.
good luck!