I can tell you that you can do both to an extent. All models work for themselves and can have an agent to promote them and can promote themselves or both. Many models starting out must promote themselves to get into the industry. There are some agencies who may see a possibility but will tell you you need test pictures. They will not provide them but may suggest a photographer. You most likely will have to find test photographers on your own but that is not hard to find by searching TFP photographers.Now, the major agencies if they choose to represent you, may require a contract of exclusivity, but this is not always a requirement. Smaller boutique agencies usually don’t ask for exclusivity, and you would be free to book with other agencies with similar contracts as well. The benefit of the agency is that they have the clients that you could not get on your own. The lower paying clients who would only pay, say, $150 for a two hour shoot, while for you would be money, the agency would only make around $30 so they would rather not spend time finding clients like that. The agencies usually make up to 40% of the payment (20% from the models pay, and 20% service charge to the client) some only take 20% from the model. The main thing is to READ the contract! Many models are so happy to be signing, the don’t read the contract that well and they don’t ask questions about its terms.are beautiful people in there establishment to help increase their popularity and visual stimulation on social media. And they actually pay very well.

Source: For someone that wants to make extra income on the side, is it more worthwhile to be a freelance model or sign with an agency? – Quora