i think that you should never pay in advance if you do not know well who you are paying to. if you are offered a two or three month Spanish course and you are asked to pay all the money beforehand please think twice as you could easily be giving your money away.

a qualified teacher would never ask you to pay any money in advance. furthermore, you should be offered to have one or two free lessons so that you both can get to know each other before working together.

beware of people with no teaching qualifications or experience offering Spanish lessons. with Europe's highest unemployment rate and so many foreigners wanting to learn our language it comes to no surprise that so many Spaniards are trying to make their way teaching their own language. unfortunately for you, not every native speaker of Spanish is a teacher of Spanish.

private lessons are expensive. definitely not as much as in Japan, Britain or usa, but do not think that you will get anything but a very bad quality tuition if someone is giving you one to one lessons at, say,  6 € per our.

 we have a saying here is Spain:    "LO BARATO A LA LARGA SIEMPRE SALE CARO"  (cheap is always expensive in the long term)

think about it.