For weeks now, Victoria’s Greens and Liberals have been privately professing their willingness to do a deal, with each accusing the other of not being serious about it. The other day it finally came through.

The Greens will run open or split tickets in 28 of the state’s 88 lower house seats. In return, the Liberals will direct preferences to the Greens in the four inner-city Labor seats they are targeting: Melbourne, Richmond, Northcote and Brunswick.

As deals go, it’s pretty limited. Neither party gets what it most wanted: the Liberals had already shafted the Greens on upper house preferences, and Greens preferences will still go to Labor in all of the government’s seriously marginal seats: the split tickets only kick in above 4.8%, and despite a certain breathlessness in this morning’s polling it’s unlikely that Labor will be troubled much in that area.

Nonetheless, a number of Liberal MPs will be breathing easier this week. Greens preferences will be split in more than two-thirds of the non-Labor seats (18 of 26), including all but one of the seven most marginal (up to 2% – Bass is the exception). And it would be a big feather in the Greens’ cap to win Melbourne, where they are now regarded as favourites to unseat health minister Bronwyn Pike.

More important are the deal’s future implications. With next year’s federal election in mind, it was important for the Greens to show – in the face of scepticism on both sides – that they can deal with the Liberals. Nobody expects them to like each other, but politics is a practical business, and there are practical reasons why those channels of communication should be kept open.

But the most important message is for the ALP. As long as Greens preferences reliably flow their way, they have no incentive to give the Greens anything in return. The Greens simply have to be able to credibly threaten retribution in order to be taken seriously.

If one or more Greens misses out on an upper house seat because of Labor’s decision to preference several micro-parties – including in some regions the DLP – ahead of them, then this will become a serious issue.