From your question and how you have framed it, I get you find Agressive Sales tactics disturb the buying process for you. ;)
I understand because I also find the whole process of Research / Negotiating / Buying / Owning / Using is all on one continuum, so anything that ruins the process will likely lose the sale or enjoyment of the item, at the end of the day.
[Very long answer .... Sorry :) ]
The answer to this is to KNOW what you want before you have to deal with the Sales people. A good Sales person likes a customer who knows what they want.
I would suggest that you follow my 'Buying Process' (Much you have already done) :
Before you Buy:
Identify the item you want and the max/min 'realistic' price you
would buy at. [Stick to this price else 'Buyers Remorse' may bite
Write the questions you have down on paper before you visit the Dealer. Write the answers you want on the same list, if known.
Decide which questions are most important and therefore must get the answer you want. These should be the questions you ask first. Mark these on the list.
Re-visit points 1-3 are they complete and to your satisfaction ?
Would you buy if all the answers & the price are right ?
If NO then re-visit point 1-3 else you are not ready to buy now !!!
If YES then Organise your visit to the Dealer. [Book appointment etc if needed.]
Meet your Sales person and clearly state what you want (the item) and importantly when you intend to buy, if all your questions are answered to your satisfaction. There is no need to discuss price at this point as the 'haggling' is only possible IF the questions are answered to your satisfaction.
Do not give information such as your maximum budget or similar requests, as they give the sales person the upper hand to maximise his/her pricing.
If asked state that your budget is conditional on the answers you get.
As the questions are answered assess the answer and assign +/- to the question on your list.
If any of your most critical / important questions are answered in the negative, they are the reasons you have to call it a day and walk out.
You can assess whether they are worth ignoring but you will need to factor this into your price and if you have identified your questions correctly there should be little room for debate.
Assuming you have got all your questions answered you should know what you are buying and have assessed what is a reasonable price for it, if you still want it as this point.
If you have lost interest, say so and let the Sales person go. Don't waste their time. They may make some sort of offer to you BUT don't forget that if you have doubts now they will not go away easily no matter what the 'great' price is.
If you want it then continue.
Buying your Item:
[None of the following is really usefull if you have told the Sales person your Budget, as they will be aiming for the highest end of your budget. You will often find that the best price is very close to your maximum budget !!! :)]
Do not forget your realistic price range, this should limit your buying price no matter what tactics are used by the Sales person.
Only you know what you are prepared to pay and if an extra 1% or 50% is considered worth it to you, if you have to have the item :)
Regardless, you have to have some idea of your limit and be prepared to stick to it. You must be able to walk away if the price is silly and not worth it.
Assuming you have not been smitten by your item and funds are NOT unlimited, ask for the price and assess it against your price range.
At this point I can only offer pointers as there are no 'magic' rules to get what you want at the lowest price. The only advice I would offer is that you will be lucky to get something at your 1st offer price unless the seller really needs to sell, because of this your 1st offer should be less than your price range lowest band. You will need to assess how much less but be prepared to get a 'No' response.
If you get a 'Yes' and your research is good 'Buy It !!!'
If you get too enthusiastic a response, question your research & if not sure bail out [No Sale] :)
At this point you are likely to be 'Haggling' so you need to be ready for all the 'Must buy Now' tactics. If you have clearly stated your wants and timescales there is no reason to be pulled in by these tactics and they can be ignored until the price has reached the level you are happy with.
If the price is not moving where you want than clearly state you cannot 'buy at that price'. If you get a total stop and no movement than you need to assess your 'need' and if priced too high then you should walk out. Remember if you stated that you had a timescale to buy of 1/2/3 weeks you should act like you have 1/2/3 weeks to keep looking. Any eagerness on your part will tell the Sales person that you have lied !!! :) You can always come back and try again, reminding the Sales person that the 'item' is still there and perhaps it is priced too high to sell and make the same offer. !!! (A bit of cheek sometimes works.)
If the price is close and you still want it and the Sales person is not moving you need to try walking out while stating that you would love the 'item' if it was priced better, if no improved offer as you go, try an increased offer but again you need to assess how much and remember you can only go up, or walk out and come back another day.
If the price is at a level you are happy with then you should have no reason not to buy (if you have followed this process) but this does not mean that you should be forced into buying now if you do not want to. Regardless of any 'Must buy now' tactics if the price is right and you cannot buy now, tell the Sales person when you CAN buy and see if you can get an agreement with this.
It is unfair to expect a price to be held for an indeterminate time, so you do need to state when you could buy if not now when a price has been agreed.
This is a point where the deal may break down if the Sales person thinks they have a sale and trys to force the Sale now. Once again you have to assess your 'need' and whether buying now is better than walking out.
If the deal breaks down there is nothing stopping you from coming back and offering the same price when you can buy.
A final option is to agree if a deposit can be left to reserve the item until you can buy. This gives the Sales person some assurance that you will come back and is sometimes NON-Refundable unless you agree otherwise before you pay, so check this detail first. (This tends to be smaller Dealers but generally in the UK the large companies offer refundable deposits as part of their Customer Service, the advantage of using larger Stores/Dealers etc.)
Apologies for the epic reply, hope it helps.