An option to filter out offers by minimum price would be sufficient. Introducing price floors would decrease number of offers which the site doesn't have much yet.
I don't think this is such an effort to filter offers, you would just need once to setup a preference to not show certain type of offers you're not interested in (e.g. show only top 20%).
What do you mean by quality of the offers? Maybe you just want to eliminate cheap competition which has better quality/price ratio?
There may be demand for cheap services in developing countries and there may be people willing to work for such money there. Wouldn't you want to receive cheap service yourself? Cheap doesn't always need to mean poor quality.
If someone wants quality work done he is probably aware he won't get it for 1 BTC, but maybe it would be enough for him.
Bitcoin was created for freedom of exchange and any limitations would hurt the market.
As a general rule, you get what you pay for. Further, allowing anything on the site is going to lead to the same problem as all the others: as a developer you open the page to see an endless sea of requests to make a facebook clone for $5.