Selling in general and especially advertising service is one tough job which you will realize only after you enter it.
The objective of advertising and marketing service is to bring customers to your clients. No matter how hard you work and deliver your service optimally, if your client does not reciprocate at the same frequency you will end up losing some or whole part of the volume of the order of your client. So it is very important how you communicate and educate your client on how advertising works. Often clients may misjudge you as a person or your company when the advertising methods or services suggested or given by you do not work for them. They may not consider the heart & soul you have given to your effort in delivering the service you were to give.
The scope of work of Advertiser is to ensure that the message of your client reaches to the maximum and relevant audience but the conversion part is dependent on various parameters which may define the fate of your service in the future plans of your clients.
But do not worry too much on the above. If you have been honest and clear in your communication and then in your work, you will surely find excellent clients who will not misjudge you. Rather they will give you more space to work and experiment.
“Half the money I spend on advertising is wasted, and the problem is I don’t know which half.” – Lord Leverhulme
This line I like to quote maximum and it answers your question in real sense.