I always use this as a get out
And that's why so many of them do it. If they've spent two hours giving you their spiel, any objections you raise will be met with answers (whether justified or not) and pressure and reasons why you shouldn't decline after all they've gone through with you. If you say you need to check with your husband/wife, that's an instant get-out that they simply cannot gainsay. It may be that they're being pushy or it may be that you are wasting their time.
Of course, as per the many examples in this thread, there is a lot of outrageous sexism; but I don't think you can blame them in the least if they ask if it will be a joint decision, then if you say yes, they ask who the other person/people is/are and say that both/all of them will need to be there before they're willing to discuss it with you.
If you say that it isn't a joint decision - that you maybe are married, but you have sole authority to make the decision, that should be respected; but then, you have no justification at all for coming out with the old "I'll need to speak to my husband/wife".
To be fair, some companies/tradespeople probably do get people insisting that they can make the decision alone, but then they play the 'spouse card' at the end anyway. Maybe because they're pushy, maybe because somebody has wasted their time and misled them.