I am looking at a 2010 ford focus with 223000 miles on it already is it worth getting?

NEVER buy a high mileage Ford

They have weekly failures at 1/3 that mileage

No. Save your money for a vehicle with way less mileage.

Is it a rust bucket Ford?

Wow that’s almost to the moon! 3700 (£ or $?), is way too much even if everything had been replaced at least once.

Check and compare...with another car of the same year & SEE what the mileage is on it.  It will be different.  Now you are looking at 2 entirely different cars.  One is worn out and one ain't worn out as much.   It is like going out with a girl who has flucked every football player on the team  ... and the other girl has been with only 1 or 2.  One is tight and the other is not.  Which chick do you want to be with.?

That's absurdly too much money for a high mileage car. For that age of car, a mileage total over 130,000 miles would be cause to question the deal.

yes for junk if its cheap enough ..give him $1,000 to take the junk .at 230,000 miles it needs a new motor , tire , brakes, new screen and that might make it drivable .tell him to get another sucker .

NO.  My personal rule is I never by a vehicle with more than 50,000 miles on it.

the mileage cars can do seems to have decreased.  They used to say diesel 250K and petrol 150K - but that was in 2000.

In any case, that's a big mileage.

#3700 sounds ridiculous - shop around

I got a brand new car in 2018 for £10,000 + 5 year warranty.  

A dealer would ask 1/2 that price and expect you to negotiate it down.