Rule No. 1: Never pay money to a model agency. Do not join an agency if you are expected to pay a fee (e.g. for joining, membership or to have a portfolio produced). Reputable agencies never charge their models any fees. They make their money from finding paid work for you and taking a commission.
Always research the agency on the Internet (do a search for their name) to see what other people say about them. Concentrate on notice boards and similar sites that provide a discussion platform for models. Your research should be thorough and comprehensive.
Legitimate model agencies have offices that you can visit, and printed stationery (some less reputable outlets do, too).
Legitimate model agencies employ staff who you can talk to on the telephone. Don't just fill in a form on a website to sign up. Pick up the phone and speak to a human.
Reputable model agencies would not dream of signing you up on the strength of a photo and some details submitted over the Internet. They will want to meet you in person.
Do not be taken in if an agency contacts you because they have seen your picture somewhere on the Internet. Agencies do that (even good ones), so it's possible, but be extra careful in your research. Be also wary of spotters or scouts.
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You should also not have to pay for casting and test shoots or for updates via e-mail or SMS.
If an offer to join an agency comes as a time-limited offer, possibly with a discounted fee, run as far away as you can. Reputable agencies will not try to push you into making a decision - do not fall for the line "we have been looking for someone like you and, by the way, we have a paid job for you, but you need to sign now".
Agencies at the very top do not require you to have a portfolio. If they sign you up, they will produce photographs with no cost to you. Other agencies may not have the financial backing to do that and may ask you to supply a portfolio. By all means, let them advise you on the type and style of photographs you should have, but be wary of agencies who want you to pay them to produce a portfolio for you.
Shy away from agencies who want you to get a portfolio produced on a prints for time or time for CD basis. If you have worked with a photographer for time before you contacted an agency, that's okay, but reputable agencies always pay photographers for portfolio work. If they try to cheat photographers, they will try to cheat you.
If you are approached by a spotter (or a scout) in the streets, do not give your details initially. Say you need time to think about it, take their details, check them out and, if you are satisfied that you are dealing with a legitimate agency, get back to them. When you do contact them, find their telephone number on the Internet or in the telephone book. Do not rely on a number that you were given. Reputable agencies will respect your vigilance.
> Read about model agency spotter scams
If an agency seems to issue guarantees of paid work, challenge them. Nobody can guarantee your success.
Before you sign a contract, read it carefully. Discuss any concerns you have. If there is anything in the contract you are unsure about, ask for an explanation. Be careful that the contract does not ask you for money. Check that the agency on the contract is the agency that you think you are dealing with. In all but the most exceptional circumstances, contracts are legally binding.
When it all does go wrong and you have paid a fee but are not getting any work, you have very little chance of getting your money back. Admit to yourself that you have made a mistake and move on.
Reputable online modelling sites, such as OMP and Musecube work differently. They provide a space for you to show your photographs on the Internet, but they do not (and do not pretend to) actively look for work for you. Usually, they offer some sort of free, basic portfolio and charge a small fee for something a little more sophisticated, and that's okay.
Sites such as StarNow.co.uk (see the two little ads just below) have information about castings not just for models but also actors, extras and television presenters.
If you are planning to market yourself through one of those modelling sites, go for the big players who attract big traffic on the Internet.
Legal disclaimer: The above comments are my personal opinion. My comments are only of a general nature and do not refer to any particular agency.