To say that someone should not have trading experience to be in the DefaultTrust network is ridiculous. If they have no experience trading then what would they be doing looking at marketplace threads where the scams are going to be taking place?
No, having trading experience shouldn't be and is not a qualification for being on DT.
What would they be doing looking at Marketplace threads then? What incentive would they have to have to be reasonable with individual trust ratings? If they have no trading experience then why would they have sent any trust ratings?
AFAIK the qualification should be that
the person is trustworthy and
the person leaves reasonable trust ratings
Past trades may indicate trustworthiness but it isn't the
only indicator. Well, theymos and BadBear isn't on DT because of trades.

There are DT members with 0 trust score and quite qualify being on Default trust than many others.
How is anyone suppose to know that you are trustworthy if you have never been trusted in the past?
Theymos may not be on DT because of the trades he has done in the past, however he has conducted business on the forum in the past. For example he
sold a TI-84 Plus with a Pink Faceplate, and he auctions off forum advertisements multiple times per month.
I am not sure what trades BadBear has conducted in the past, however he has been trusted with sensitive information in the past (and AFAIK continues to be trusted with such information). He also trades his services as an admin for several BTC every month.
to doing lot of successful trades.
Past trades is not a guarantee of trustworthiness, though it most of the times have to be taken so because there are only less things to base it on.
theymos isn't on DT because he sold a TI-84 plus with a Pink Faceplate.
the person is not untrustworthy, has not indulged in suspicious behavior and can be reasonably trusted; and most importantly