@jackty89 it actually depends on the country. I don't know other country's history that much, but I can at least say that it's not true in France. In France a nobility title could only be given to you by the King, and then your offspring would inherit it. You couldn't buy your way into nobility, which was actually the major reason why the Revolution started in the first place.
A lot of noble families ended falling apart as time go by, so much that a lot of merchants were actually richer than the usual noble in France. The country was mostly run by the Bourgeoisie (rich tradesmen, etc), but they still couldn't buy themselves into nobility. The nobility was still privileged and had more political power than the Bourgeoisie, even though they had less economical power. It ended up upsetting the Bourgeoisie, and that's the gist of how the French Revolution started.
Though this is a fantasy setting so let's not make historical comparisons, it could totally be possible to buy your way into nobility in this fantasy.