First and the foremost welcome to BMW community, secondly please dont compare Accord with 520i. You can never get that umph, punch, driving pleasure, control, respect, style, design, safety, confidence in any Japanese car as you can get in any BMW. You are simply comparing a wrong league. I am not saying as im also BMW fan or im speaking in BMW community, but truly i mean it as i realized this over time.
Buying used car here in Dubai, my personal choice would be buying car ONLY with full service history with AGMC or with any other competent workshop like Tony edwards or Munich motor. You can give a call to these both BMW specialist and get an idea on service cost before you take a dive. Good luck and go for Bimmer anyday.