Interpretation of the term "pretty active".

Pretty may act a mild intensifier - in ascending order of hardworkingness: he works hard, he works pretty hard, he works very hard. As you seem to be aware, in a reference any qualification of praise could be intended as a thinly disguised criticism, to damn the candidate with faint praise, for example like saying Joe Smith works 'fairly hard' when a recruiter really wants to see 'very hard'. However we do not know the background of the person providing the reference - are they a fluent English speaker? Do they come from a British English background, where faint or less-than-heartfelt praise are sometimes ways of politely criticising someone?

This could all be about nothing - they could simply mean he works very hard. In a situation like this, an astute recruiter would telephone the provider of the reference and seek to have an informal chat.

I asked my wife, who reads references all the time, and she said "Pretty hard? I'd wonder why it is qualified?"

Perhaps you need to think about your performance at the job in question?

On a humorous note, I once read a British reference which included "If you get this person to work for you, you will be very lucky".

Positive. It meant that you were engaged with your tasks. What can be interpreted in another way?

I think I would rather hire a hard worker than a pretty hard worker.

"We found John pretty active in whatever task we have provided him with."

I'm asked to write reference letters pretty (ha) often. If I had written that sentence, I would mean that John is an intermediate worker. Not bad, not excellent. Acceptable, maybe, but it's not glowing praise, either.

There is a phrase in English: "damned with faint praise".

Bingo. That's what I was trying to think of earlier.

At IBM (I believe it was) they had an entry like "So & So is 'well placed'." That meant So & So could forget about further promotion.

Ah-ha. I think I'm pretty well placed, then. And happy with that fact. Anything higher than where I am carries a ****-ton more responsibility with hardly any increase in salary. I don't go for that ****.

Nodding.

Reading between the lines is a valuable asset for a hiring manager.