The way I see negotiations playing out with the eu is that both sides want as much as they can get.

On a scale of 1 to 10, 10 is free access to the market,control over immigration, no tariffs, no membership costs, etc, etc.

1 is high tarif access to the single market, free movement, membership cost, no say in what goes on, etc, etc.

Negotiation should lead to a 5 or 6, but if the eu think that May is under pressure at home, they will think that they can achieve a 2 or 3 and that the liberals and remainers will force her to accept it. However, if she wins the election with a large majority, the eu will recognise that she has the firm backing of the country and will know that we will prefer no deal rather than anything less than a 5 or 6. Whereas we know that German and French industrialists will be pushing for a deal, even if it's a 7 or 8, rather than no deal which would be extremely damaging to them.

The only problem is that it only takes one small country to insist on a 1 deal, to scupper the whole deal.

Ironically, voting liberal will actually mean voting for a poorer brexit because it would mean undermining our negotiating strength.