AusBonsai

So I bought this tree today and would appreciate some advice on where to take the tree From here. It has a good base and 3 straight trunks. should I cut the trunks back and regrow them or just develop it from here. I’m thinking I want to cut it back and regrow them but what do you guys think?

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Shorter would make a more dynamic tree IMHO so I'm for cutting it down.

I see a tree with 4trunks. I see another bare root tree with 3 tall trunks and I see a tree with 3 shorter trunks and some good regrowth.

I assume you are referring us to the taller 3 trunk bare root tree.
Cut the trunks short. Trees tend to bud strongest near the top of the trunks. If you leave them all tall ow you will only need to do another trunk chop later and the tree will be set back again.
Cut them even shorter than the planned final bonsai because trees almost always grow up and bigger so cutting at finished height will only give you a much larger bonsai than planned after the new parts grow out or you will need to chop again and set it back.
With multi trunk the trunks look far better if they are different heights - Thickest trunk is taller, thinnest is shortest. The other 3 trunk olive shows good proportions.

Ok it’s getting cut back, how short are we talking ? Reduce them all by 2/3 put in back in he ground? And re grow the trunks And get better taper and movement Or just reduce the height Enough so once the new crown is grown it will suit the final height?

There could be a number of options depending on what you want at the end.
Dead wood is common on really old olives. Shari is an option to give simulated taper to a trunk and taller sections could become jin but I don't think you want really tall jin on olive. Just a bit above final foliage height would be ample and can always be reduced if it looks odd.
Hollowing out one side of a trunk is another way to induce taper. It is much quicker than growing taper but carving is not always done well.

If you decide to reduce the trunks and regrow you are the one who needs to decide how much because it is you that will grow and look at this tree. Rather than looking at how much to take off look at the base and trunk and decide how tall you imagine the finished tree would look good on those trunks then cut to suit. Either to allow for dead wood as above or to allow for regrowth to give a tapered trunk in 5 or 10 years. Olives don't usually grow very fast.