The way of selling services is in an informational way that targets the people to whom the service will be provided.
Most of the services are provided between companies, so LinkedIn may be better than Instagram due to the presence of most company’s managers.
However, you can use Instagram and target companies that you can solve their problems through your service. For example, if you are a web designer, you can see the sites of the companies placed in the Bio, and if it is bad, you can provide them your services and solutions to develop them or create new sites for a symbolic amount.
If out of every 50 companies, one agreed to you, then you found a client! And the rest of them may talk to you after a year or 10 when they need to change their sites because you showed yourself.