In reply to OneLifeOneHeart:
Buying rock shoes is always a bit problematic even when you have years of experience but it is very hard at the start as you don't know what is acceptable 'pain' etc.
Basically, as a beginner, don't buy rock shoes too tight. What you want is a fit where the shoe is fairly snug all around your foot and you don't have big air pockets, loose bits, or your foot just rolls around in them. As you seem to appreciate, ideally your toes will be slightly bent but not so much that it is painful. This helps give a bit of tension in the shoe and also feels more precise. However, as a novice that's not going to mean too much to you so don't overdo it.
Remember that most shoes will stretch a little and become more shaped to your foot after some wear. If they fit well, even quite technical shoes can become very comfy.
I would echo the above comments about La Sportiva shoes being sized very roomily (I wear them about 2.5 to 3 euro sizes smaller than my street shoe for a semi technical fit). But all of them are different and your street shoe size is only a starting point. Use the comparison chart someone linked to above to help size particular shoes. It will tell you how many sizes to go up or down from your street shoe to produce a spectrum of fits from comfort to very tecnhical (and you want to err on the comfort side). Even if the particular shoe your are looking at isn't shown, you can see that most makes of shoe have a particular trend re sizing which should give you some guide.
Try lots on and go for what fits you best. Some so called technical shoes are actually very comfortable on some people (eg. 5-10 green lace-ups are great for people with narrow'ish feet) so don't totally ignore the higher end shoes. Having said that, you are probably best off going for an entry level shoe with thicker rubber (lasts longer) and probably rather stiffer to support your feet more (whilst your feet get stronger).
As for the comments made at the shop you went into, they may have gotten frustrated if you were just asking their advice constantly and not helping them with appropriate feedback. Yes, they are there to give advice but, on the other hand, only you can tell how your feet feel in them and ultimately you have to make the decision.
I would take a little time looking at the sizing chart link and working out what would be a comfort fit in a shoe you like. Use that as a starting point but remember that everyone's feet are different and you should go with what feels right for you.
One final point, try them on in the afternoon or early evening when your feet have swollen to their normal maximum size (though they will get even fatter if you climb outside in the sun!).
As all good shops will let you try them on at home again and return them if you've not worn them outside, when you get them home, try them on the next evening and wear them for an hour or so and see if they feel comfortable enough without being too roomy to be much use.