C. If they make unrealistic promises like 'guaranteed fills even during news events' D. If they make claims like 'biggest forex provider in the history of mankind' E. If they try too hard to get your business regardless of how little you plan on putting into the account / or your experience as a trader. ie. they ask to call you within 30 seconds of showing interest and give you a sales pitch over the phone.
I love bucket shops with FREE Meta on demo accounts, great free real-time software for TA. What a fantastic way to save money
F. If you can fund your account with a credit card G. If you can't find a physical mailing address on their website H. If they have cheesey actors on their website posing as operators, business owners or worse winning customers
I still don't understand how the OP doesn't know the basics of how forex works. You can't trade what you don't understand.
if you want to trade eur/usd, for god's sake why don't you trade the futures. I trade gbp/usd-futures and make a decent living at it, so yes it's possible.
J. If they charge you to send you your money back and there is no other option to get it back for free.