Going back up the thread a bit, On tendering internationally: because contracts have to be advertised internationally, doesn't mean that you have to accept a foreign tender just because it is the cheapest. There are many reasons for not accepting a foreign bid - or a local bid, for that matter; doubts about quality, line of command, lack of track record etc etc.
When I worked in industry the contracts I let were low and came in under the international threshold, but with a range of bids from UK contractors, I didn't necessarily take the cheapest. Providing you have a document explaining how you reached your decision - and you should do that for any contract anyway - there shouldn't be a problem.
One of the negative factor considered when tendering for a waste incinerator in my county was the fact that one of the companies involved had a very poor record of compliance with environmental regulations controlling emissions at other facilities it owned and operated.