I am considering buying a Lexus LS430 with 100K miles. Should I be concerned about maintenance

If this car was well kept 100k in nothing. Check out this link it will give you some ideas on what to expect in the future

http://autos.msn.com/home/reliability_ratings.aspx

Anything above 100K, l would be weary of, even for the LS430 which has historically been one of the best in realiability. 100K is a lot of miles to be driven if the previous owner had a lead foot, did not main well, or drove it in a lot fo stop-n-on traffic & rough roads.

With that said, if the LS430 was well maintained, it should run to 200K without issue. Some more, OPTIMISTIC, people here like to think that it will run to 600K without issues, but that is being too unrealistic. Aim for 200K & if u get to 400K, it is gravy, & 600k is just WOW.

Darth, l am telling you man, 600k is not as high a mark as you make it out to be. 100k for the LS430 is cake.. go change the timing belt, spark plugs, maybe water pump, check suspension components. These cars are as reliable as any car can get. End of story.