I went to the lot and they have a 2005 GS300 for 4200$ it has 230,000 miles is it a deal

 

That's high mileage, but a pretty low price. What kind of shape is it in? What's an average price for a GS300 in your region? We have absolutely no way of knowing if it's a good deal for you with the information you've provided.

 

Are you kidding me, RUN away from it man !!
This goes for ANY car with that high mileage.
These cars do last LONGER then that but who knows how much longer.
There's a reason why it's being sold.
Rather, use that $4200 as a down payment on a $10k used GS which will get you something with less then 100k miles.

 

This is a Lexus bro. Not a Chevy...
100k miles on these specific cars is not bad.

We've got people on this forum with 300-400k going strong no problems!

Make sure the maitenance is up to date & the previous owners have taken care of the car ( clear title...no accidents, verifiable service records, newer tires and brakes, ball joints replaced, timing belt etc) before you decide to jump in.

If they did all that, the GS can easily last another 100k without any major maintenance needed.

As for the O.P,
Get the carfax and if everything checks out, offer them 3950.00 and see if they bite