I have received an email from an advertiser who wants to run ads on my site. He told me that he would need me to create an extra subdomain for his ads. This sounds strange to me. Did this ever happen to you that an advertiser wants his own subdomain?
Sounds strange to me. But as long as you don't give the person access to your site, there should not be any problem.
If an advertiser contacted me with that kind request, I'd brush it off. UNLESS, it was Target or Sam's Club or something like that. Is the advertiser paying you up front? Because you can end up going through all this hassle for very little or nothing.
Here is a quote from him: Sure I would request an upfront payment since we already set a monthly price but I am hesitating now since he made the subdomain request after everything else was okay.
It could be legit - what I'm thinking is they need to run a script and they can only do it off your domain to avoid cross-domain issues with scripting.
I think it is most likely legit and you wont have any problems in using it, but as Devtard has said above, do make sure that it is entirely safe before using it.
It seems like that they need it for their search form, so that they can style their advertising results equivalent to my site (?). Whatever the reasons are, the effort combined with a little risk on my side is bigger than the profit. Therefore, I rejected the advertiser's offer.