As soon as they say that, don't bother replying; just delete or block. If you're bored, string them along, and come up with the most outrageous crap you can.
Scamming scammers is fun. :-D
I would suggest OKCupid, if you're looking for long term. I'm just someone who has used the site, not...
Whatever site you're on, in your profile put the following (or words to this effect):
I am not your sugar daddy. I am not your pocketbook. I am not your free ride. When I find the right one, She will appreciate that I did not spend my money on whores. Don't be a whore.
It gets the point...