Payment BEFORE or AFTER ad delivery?

CPM based advertising

[jasonlambert]

Situation:
Selling advertising on a content site on a "cost per 1000 impressions" basis, in an industry where the CPM rate is generally "high".

Example:
Lets say you sell agree to deliver 500k impressions at $40/CPM to a company who has never advertised on your website previously.

Question:
Assuming you are financially stable, and not receiving the money in the next 24 hours is not going to cause bankruptcy - How should you handle payment terms? ie:

- request payment before serving any ad impressions;
- wait until all the ad's are served then send them an invoice;
- start showing their ad's, but request payment is to be received within 30 days of start of contract;
- request XX% up front deposit before start of campaign, and rest of money upon completion;
- Other?

Any thoughts or experiences you can share?

[Yidaki]

You could

... offer them a 4% discount if they pay in advance.

... offer them a 2% discount if they pay within 14 days after campaign start.

... offer them to pay 50% in advance and 50% after delivery.

... offer them the possibility to pay after delivery for future campaigns.