The HQ Sweet 16 is a sweet machine.
Ask why they are selling it. ($2k is a lowball price). I've seen them for $3,800.
Ask what version the software is. If you want to ever use it with the TruStitch regulator, it needs to be at a certain revision.
Ask if it has the regular foot or the open toe foot.
Ask if it includes just the table or if there are extensions.
Ask if the bobbin winder is included and if it is the industrial-looking model of winder.
Ask how many bobbins and what extras (if any) are included.
It requires a special oil and special needles.
BTW, there is a YAHOO group dedicated to HQ Sweet 16 - you may want to join.