[3/46]
Did Seetaa recognize Raavan as a fake Braahman or not... is the doubt raised by this verse, because different texts use different compounds. But it is concluded that She, for sure, identified him as a fake Braahman, because She had seen many such Sanyaasee in Mithilaa, (She is called here as Maithilee because She is from Mithilaa) and her father's court was full with these Sanyaasee, Yati etc. Then it is questioned as to why she invited him, in spite of recognizing him as a fake Braahman. For this it may be said that 'By spotting the saffron robe alone, a Sanyaasee is venerable...'

Then, another doubt is raised as to how did She notice him to be a fake Sanyaasee. For this, first we should know who are fake Sanyaasee? It is said that "Walking during night, using vehicles, showing interest in episodes relating to women, and keeping relations with women, using a bed to sleep, wearing white cloths... these six characteristics show the downfall of his Sanyaasee-hood..." Since Raavan was indulged in talking about women in the whole of this chapter, "in admiring at her lips, breasts, thighs etc., and no usual Swasti Vachan (greetings), Shubh Aasheesh (blessings) etc to Seetaa" are uttered by him. Therefore Seetaa could discern him to be a fake Sanyaasee

If She knew him that Raavan was a fake Sanyaasee, then why should She revere him at all, is another question. What else she could do? Because his appearance itself was doubtlessly irrefutable hence, She tried to gain some time until Raam or Lakshman could come. Otherwise, this fake Sanyaasee might cause any kind of problem that She could not solve. [Although they couldn't come by then]

The reply of this is at the end in the last verse - "only greenery is seen by Her not Raam nor Lakshman...' And in the next verse itself she is addressing him as a "Braahman...' but not with the titles like Sanyaasee, Yateeshwar or Paramhans or Parivraajak etc. Only Braahman alone is eligible to take up Sanyaas (the Hindu-Sanyaasee-hood...' not Kshatriya or others). Hence, She concluded him to be a Braahman. So when once the Sanyaasee-hood was taken away he was no more a Braahman and his physical appearance was neutralized in the Absolute (Parameshwar), and such a Sanyaasee shall drag on his body, without comfortable physical needs, until his natural death. But Seetaa was addressing him contrary to this.

[Taken from Valmiki Ramayana 3/46]

Although Vaalmeeki Raamaayan never mentions any where the story of past life of Raavan, but if we read Tulasee's Maanas, it clearly says that Raavan and Kumbhkarn - the gatekeepers of Vishnu, were born on Prithvi because of Sanakaadi Muni's Shaap when Sanakaadi Muni came to Vaikunth to see Vishnu and His gatekeepers - Jaya and Vijaya, did not allow them to go in. Then they gave Shaap that "You be born as Raakshas on Prithvi because you are not worthy to be the gatekeepers of Vishnu's palace." 

At that time Vishnu promised to save them from this Himself. They were born on Prithvi three times and Vishnu also had to incarnate four times. Vishnu saved Hiranyaaksh in the form of Varaah Avataar, and Hiranyakashyap in the form of Nrasingh Avataar in Sat Yug. He was born as Raam and saved Raavan and Kumbhkarn in Tretaa Yug. He incarnated as Krishn to save Shishupaal and ..... in Dwaapar Yug.

Since Raavan was Jaya, many commentators argue that he was a great devotee of Lakshmee Jee, that is why he blames Seetaa for all this episode from the very beginning, because according to Raavan Lakshmee is the inner-force in everybody's heart and She worked in the interest of Raavan from the very beginning - right from Raam's going to protect Vishwaamitra's Yagya, receiving many kinds of weapons, facing Maareech but not killing him [maybe He knew that He had to see him again], then Dashrath's right to coronate Raam  but still not being able to coronate Him [he could have exercised his authority, but he did not], Kaikeyee's asking of Var at the same time and that also Bharat's kingdom and Raam's exile [it is well-known that Kaikeyee used to love Raam more than Bharat], then Seetaa's coming along with Raam to forest.

Even their coming up to this point of the forest [otherwise they could have gone back to Ayodhyaa easily after spending their 14 years of exile just staying outside their kingdom] was also because of Lakshmee Jee. Arising the desire in Raavan's heart to abduct Seetaa which resulted Raavan contacting Maareech, forcing him to lure Seetaa in the form a Maayaavee Mrig, sending Raam far from Seetaa, then Lakshman on the cry of Maareech to create the perfect environment to abduct Her - everything was guided by Lakshmee Jee.

[3/48-49] 
He offers Her all kinds of highest respects and asks Her - "Why don't you come to my Lankaa, so that Raam can also come to Lankaa following you to destroy all Raakshas, including me, for which He has incarnated in human form on Prithvi. I will be your good servant [Vaalmeeki has used "Bhartaa" word here for Raavan which means husband, but it also means servant. So Raavan has used it here as Her servant]. But people take it as husband.

"Although I am your foolish servant but grace me too as I am your long serving servant. Raam is not fallen from kingship. When He is the king of Trilok why should He care for such a kingdom. You are in love with Him, I have no objection in that but bless me too. So please come with me to Lankaa so that He can follow you and accord me salvation as planned by you all."

He pleads and pleads Seetaa to be his wife (to whom he will give the highest position being Lakshmee) so that he can instigate Raam to come to Lankaa and to take His Seetaa back. But when She doesn't heed his pleading, he knows what to do. He abducts Her forcefully still respectfully.

Although Raavan is a wicked soul and of very lusty nature, but he is lusty only for other women, not for Seetaa.