I think a lot depends on your future plans.
Property prices will always dip and rise. If you don't plan on staying for long, then negative equity could be a concern. But if you plan on staying in the property for quite a while, then negative equity doesn't really matter. Negative equity is pretty irrelevant if you've got a mortgage tied up and in place, and you have no plans to sell or move. In the long term, property prices will always increase.
For context, I bought in 2007 at the top of the market, right before the huge crash. Undoubtedly I would have been in negative equity but I didn't care, and didn't bother to check. It was my home and I was very happy living there. I've literally just gone to market - yesterday - and it's been priced at around 38% more than I bought it for in 2007. And before I'm dismissed as a greedy seller, I've gone on at the lower end which is about £20-40k less than similar houses in the same area. I've had four viewing requests in the first 24 hours which suggests my pricing is competitive. I don't mind coming down a bit either - but I wouldn't lower my price by 10% just yet. However I would take 5% lower than the listed price, no problem. That's because I want a quick sale - which is why it's been priced so competitively. (Also, although the % increase seems high, I only have a small 2-bed in the SW so we're talking prices of <£200k).
We bought our new property last year - we're buying with DM to build her an annexe. We have spent £££ on a new extension and creating an annexe. As the house market falls the house could well be worth less than the total spend, but I'm confident in the long term, the value will be significantly higher. We're not moving any time soon so short-term drops won't make any difference to us.
I'm not suggesting you go wild and buy recklessly - all I'm saying is that you can wait a long time waiting for the market to bottom out, and sometimes things don't pan out as the experts predict. I don't think it's worth wasting your life waiting for the conditions to be just right - if you want to buy and can afford it, then great. If you can't afford it, then don't stretch yourself.
I do completely agree with previous advice though - you could absolutely try a cheeky 10% below asking price offer to test the water, but are you sure that you'd be paying the right price? Whatever house you want to buy, compare it to others available in the area and see how it matches up - look at condition, work needed, square footage, size of garden etc. There's no way of taking an isolated house and working out if it's good value - you need to see what else you could get for the same money in the same area.