Apparently my mom sent all of us (and so did many other mums ...) to her to be potty trained in less than a week.
Her approach: prepare a large (!!!)
basket/tub anything and fill it with presents
To keep this manageable, presents can be small (bubbles for blowing bubbles, Mr Men book, chocolate stars, etc.) but have to be all individually wrapped.
Explain a few days before that the idea is to go on the potty each time for wee or poo and then choose a present (basket not in sight yet). Repeat this frequently for two days and agree to start on a certain day (marked on the calendar). That day give something to drink every 10 minutes and have potty standby, ask every 5-10 minutes if she/he wants to use potty and remind that will get a present if uses potty. Keep giving something to drink frequently for the whole morning. Easiest to let walk round in bare bum whilst doing this. Keep doing this for the next 2 days (you can't do anything else, have to keep an eye out all the time and keep reminding). After the first two days (if successful, we all used it with our children so far 100% successful) then you could agree slightly larger present for 3 wees/poos on the potty and slowly scale down (my dd still insisted on presents a month later, that is the expensive bit). As you will see you will need to prepare in advance, according to my grandma you should have approx 100 small presents, nicely wrapped. My daughter loved it (I found it initially very very tiring - continuous reminding, giving drinks etc, but nevertheless wworth it as she was fully potty trained in basically 1 day).