Is the question mark misused in affirmative sentences?

For example, I found the following sentence written by a native English speaker (UK) so I'm going to assume that he knows how to put it the right way, although I wouldn't use this form.

I now have a bit more time to fix bugs etc but I'm open to offers if anyone wants to help maintain this module with me?

Is it correct or is the question mark misused here?

Solution 1:

In written speech this is a questionable usage. Nevertheless, when speaking, people frequently end declarative sentences with a rising intonation to invite the listener to consider the sentence as an invitation to agreement or action. One hears this kind of thing especially in the southern United States.

"Anyway, I had this Chrysler? It had a four-barrel carburetor?"

Here the speaker is making declarations about a car, but making them sound like questions so that the listener will respond (probably nodding or saying "uh-huh") in a way that indicates interest in and understanding of the story being related.

If your example sentence were spoken this way, listeners would likely interpret it as a request for help, not merely a statement of a condition. But if you write it, you should leave out the question mark.

Addendum

Since I wrote this, I've become aware that the practice of ending declarative sentences with a rising intonation actually has a name:

uptalk n
a manner of speaking in which declarative sentences are uttered with rising intonation at the end, as if they were questions.

Solution 2:

While the sentence is not technically a question, the use of a question mark indicates that the speaker is inviting a response from others.

In that respect, the question mark conveys the speaker's meaning in a way that could not otherwise be indicated in writing without the use of additional words.

So I'd say that this use of the question mark is correct when recording informal speech like this - but formally, it should really be reserved for actual questions.