When you define someone, for example say to a girl that you have a beautiful smile(У тебя красивая улыбка) and she says: oh thanks you can answer her: "only real words!"
So is it correct sentence in this situation ?
"Только настоящие слова!"
When someone thanks you for a compliment you have paid them, it's natural to respond like this:
У тебя красивая улыбка. - Спасибо! -
Не за что(stress не to mean you're welcome).
If you really want to stress that your compliment is only natural because you are stating a fact, you may want to say
это - факт or
констатирую факт. Note that the most common way to respond to thank you is saying
не за что.
For this kind of conversation the closest equivalent I can imagine would be:
– У тебя красивая улыбка. – Спасибо. – Нет, правда!
Other examples (e.g. sentences involving
сказал правду) sound too heavy/formal for that, and (to be honest) they still look like an attempt to just translate the corresponding English example w/o considering if they talk like this in Russian at all.