It depends what is wrong with your existing blind. If it’s an old roller blind and the chain is stuck, you may just need a new chain.
Vertical blinds carriers once they get to around 25 years old tend you go brittle from the sun and it can be worth having the track repaired still.
But when we come to venetians, it’s a better option to replace the blind with a new one. Venetians get dirty over time, controls break, slats either get bent or snapped.
It can cost around the same price for a new venetian (depending on size) saving you money in the long term.