/ Pronouncing final -ą as -oł (Czech infleunce?)
In standard Polish (as described by Polish philologists I've known (and whose articles I've translated)):
The difference between ą and on, om and ę and en, em (before a stop or affricate) has been lost in modern Polish. So łąka is łonka and the standard pronunciation of będzie is bendzie (or beńdzie if you prefer).
Further, the difference betwen ą and on and ę and en before a fricative is also lost, so that the standard pronuncation of sens is sęs.
In other words, ą is pronounced nasally before a fricative (as in mąż or związek) and as o plus nasal consonant before a stop or affricate (rąk = ronk, stąd = stont)
The patterning is exactly the same for ę, en and em (często, vs wnęka = wnenka etc) except that the sequence -ętn- is usually pronounced -etn- as in pietnaście, umietności etc)
Before l and ł, ą and ę are pronounced o and e respectively. Nasalizing those vowels would sound bizarre.
Word finally both nasal vowels have a similar range of variants, but the distribution varies. In order from most to least ... elaborate.
nb. in the following ~ = vowel nasalization
1. [ou~] and [eu~]. In other words, o and e followed by a short nasalized u (or ł) sound. The initial part isn't nasalized, only the u. This is common for ą but not so much for ę (except for się when it's emphasized) and often enough dziękuję.
2. [ow] and [eu]. As above but the second part isn't nasalized. Often people think variant 1 is being used when it's actually variant two. This is why most modern speakers can't distinguish between zginął and zginą, pronouncing both as zginoł (even educated speakers who think they can distinguish them mostly .... cannot. The patterning is the same as for 1.
3. [o~] and [e~]. In other words, o and e which are nasalized to some degree. Usually the start more oral and the nasalization only happens toward the end of the word. This is common for ą and not unheard of for ę. As I wrote previously, the best style is considered to pronounce some instances of ę with nasalization and others without. The determination of which to pronounce in which way should depend on homophonic and other factors (like place in the sentence).
4. [o] and [e]. That is, like plain o and e. For ą this is considered substandard, for ę it should be in alternation with 3. or 1. and 2. (this is for native speakers only, absolutely no one really cares what a non-native speaker uses as long as they're understandable ....)
5. [om] and [em]. Like plain om and em. This is considered substandard for both, it's generally more common for ą than ę (but Wałęsa is known for the latter as in his famous quote "Nie chcem ale muszem."
1. You can sometimes hear self-conscious pronunciations like [beu~deu~] instead of the preferred [bende or bende~]. This should be regarded as hypercorrection and should not be mimicked by anyone (except perhaps for humorous purposes).
2. It is okay to distinguish ę and en in spelling pronunciations. Poles mostly don't spell words outloud like English speakers do. To clarify the writing of an unusual or ambiguous last name, they may use a spelling pronunciation where each letter has it's canonical value.