Marketing is about mass communication.
That means volume.
Sales is resale. Marketing is wholesale.
The reason of course is you are never going to get a high percentage of response. 5% response rate would be phenomenal in most cases.
Direct mail these days can run 0.1% unless it is very targeted.
If 1% of visitors to a website purchase or make contact with you, that is usually considered to be doing alright.
No matter what you are marketing, think in terms of how you can expose your product or service to LOTS of people.
If you can’t do this, until you have a way to do so that you can afford, you just aren’t doing marketing. Sending out 100 postcards isn’t marketing.