turntable arm cart £500 what's best

Dek Ittok in whatever form you can get it, and a cheap goldring cart (new).

Imho. for that kinda money there's only 1 option:
a Rega P3(with many cartridge option's like Dynavector,Rega,Grado,etc)

(considered buying new)

New - rega P3 with Dynavector 10x4 cartridge. Great combination for the price.

2nd Hand - the biggest problem here is the condition of the kit, especially the cartridge of course. The arm can be checked by balancing it and checking for any play or stiction. Any stiction and you should walk away! As to the cartridge, well, you can't check it by eye unless it's truly knackered so you have to go a bit on faith with that so I won't be mentioning them hereon. here's a few suggestions:

Any Rega 3 or 25. £150 for the 3 and maybe £350 - £400 for the 25 depending on age.

You could pick up a fairly old LP12, possibly with an Ittok (but more likely an Akito or Basic). Sonically, this can sound better than the Regas, but don't forget to factor in the extra £100 for a service and the checkup every year to 18 months at a knowledgeable dealer!

Another option could be something like a 2nd hand Michell Gyrodec. These don't need as much fettling as an LP12, but you'll probably get one with a Rega RB300 for this money which isn't a natural combination in my view. that said, it's a fine deck. (Hey, I use one.)

Roksan Xerxes (and maybe even a 10). Early ones tended to warp. Needs little fettling once setup. You'll get it with either a Rega arm or possibly a Tabriz or Tabriz-zi arm. The Tabriz arms are better than the RB300 in this situation.

Regards,
Frank.
All opinions are my own and do not reflect the opinion of any organisations I work for, except where this is stated explicitly.

THANKS CHAPS.