It is usually not difficult to pick a Nigerian scam mail. They start with Hello Dear (or sweetness or some other pet name). The English is broken with bad spelling & punctuation like it is a second language even though they say they are British or US raised. They use terms like "I am the only child of my parents", strongly push the fact that they are "God fearing", will suggest going straight to IM and give you their addy in the first contact. They are very quick to start using pet names like honey, baby or sweetheart. They don't understand western names and will often reverse them eg. Davids Robert or Smith Ian.
Photo's are nearly always stolen. They used to get them from modelling sites but have learnt that those are too good to be true and are now stealing any photo from the net to look like what they think is the average man or woman.
If you receive an off site email from them you can check the IP address. G_ogle 'header tools' to find the sites where you can enter their IP addy and it will give you the country of origin. Don't be surprised when it shows an African country instead of US or UK as they told you.
There are various sites to gain more information... simply g_ogle romance scam. There are 3 main countries with scammers, Nigeria, Russia & Philipines. Most Nigerian scammers are male but they will pretend to be female when necessary.
NEVER give your primary addy to someone you don't know. Have a secondary or throwaway addy to use until you know someone well.